Ever since the FCC began a campaign to reign in overly-powerful FM transmitters last year, and manufacturers quietly began to change their accessories to comply with the agency’s demands, we’ve been reluctant to make any definitive statements on these devices: as hard as it was last year to know for sure how well a given transmitter would work in a given car, new differences from unit to unit now increase that difficulty. But while the FCC has limited the power of these devices, it hasn’t stopped companies from improving on them in other ways, so today we’re looking at five different in-car iPod accessories with FM transmitters inside. Our standard disclaimers — that your car’s antenna location, the iPod and transmitter’s location, and local radio airwave congestion can radically affect your results — still apply.

The five accessories come from three companies and break down into two categories. Belkin’s TuneBase FM with ClearScan ($90) and Macally’s BTCup ($100)—a more expensive sequel to its earlier FMCup—both combine an FM transmitter with an iPod car mount and car charger, but vary considerably from there. Kensington’s Liquid FM ($80), Liquid FM Plus ($70), and Liquid FM Deluxe are cables that offer only the FM transmitter and car charger features, leaving you to mount the iPod on your own.

All five of these accessories have three things in common. They’re all made substantially from black plastics, although each has silver and/or gray accents. Their FM transmitter performance was universally good in our testing, with only small variations from unit to unit. And they are all a little more restricted in frequency tuning than the best pre-2007 devices we tested: all tune from 88.1FM to 107.9FM, rather than up to 87.7 or 87.9FM. This is an issue only in that the latter station has consistently been better than any other in our prior testing—it’s almost always empty in the United States because major broadcasters aren’t allowed to use it.

Belkin and Kensington both have solutions to this problem. Two of Kensington’s transmitters—LiquidFM Plus and Liquid FM Deluxe—as well as the new Belkin TuneBase FM include a feature we first tested last year, which Kensington calls QuickSeek and Belkin calls ClearScan. Most other FM transmitters, including the standard Liquid FM and BTCup, require you to find an unused FM radio station on your own, then tune the transmitter to match that station. QuickSeek and ClearScan simplify that process. With one button press on each device, the screen begins to sweep back and forth as the transmitter searches for a relatively empty FM radio station, displaying its result so that you can tune the radio to it. In our testing, this feature always worked well enough on both the Belkin and Kensington transmitters to produce relatively clear, low-static sound on the chosen stations, though the transmitters didn’t always choose the same stations, and quality typically varied a small bit from pick to pick. Overall, we think the ClearScan and QuickSeek technology is useful, but we’re not sure that it’s worth paying a huge premium for. Kensington’s assessment of QuickSeek’s value is $20; street prices peg it at $12 and up.

For more than a year, Kensington dominated our in-car accessory reviews with its long-titled Digital FM Transmitter/Auto Charger for iPod, which carried an $80 MSRP but a comparatively reasonable $53 street price at the time of our mid-2005 review. The standard $80 version of Liquid FM is a replacement for the older product, and only modestly updates its features: the old blue-backlit screen is now a higher-contrast black and white affair, while the five face buttons (manual up and down tuning, plus three presets) have been augmented by a top-mounted power button, all forming the top, bottom, and sides of a rounded rectangular box. A car charging connector is at one end, and an iPod Dock Connector is at the other. Once again, retailers are selling this Liquid FM for $50 and up.

The QuickSeek-equipped versions are Liquid FM Plus, and Liquid FM Deluxe; a silver button is added to the right side of each combination charging and FM transmitting box. Plus is cheaper—selling for $44 and up—because it loses the iPod Dock Connector in favor of a device-agnostic, standard 3.5mm minijack audio connector and a USB port for charging. You can use Plus with the iPod shuffle, but because of the shuffle’s odd charging and audio port, you’ll have to choose between doing one of those things at once, and supply your own shuffle Dock for charging. Plus also includes a 3.5mm to 2.5mm adapter for use with cell phones and other unusually small headphone connectors.

By comparison, Liquid FM Deluxe sells for $62 and up, as it’s Liquid FM plus the QuickSeek feature, and mixes black plastic with metallic flecked dark gray parts for a slightly nicer overall look. Even though we felt that Kensington’s first stab at a QuickSeek-equipped FM transmitter for the iPod—the aptly named QuickSeek FM Transmitter for iPod—was overpriced at $90 relative to Belkin’s excellent TuneFM, TuneFM doesn’t work with any of the latest iPods, and LiquidFM works with all of them.

That fact is really the Liquid FM family’s major saving grace—for now. Thanks to Belkin and other competitors, FM transmitter prices have fallen, and features improved, since we awarded the Digital FM Transmitter/Auto Charger its rare A- rating, and yet, the basic version of Liquid FM offers little more than its predecessor for the same relatively high price. Additionally, the FCC’s enforcement actions have further levelled the playing field, such that none of the transmitters we’re testing these days stands out so much from the others in audio quality as to strongly prefer one over the others on that feature alone; consequently, pricing and frills are becoming more important than ever. Overall, we think the standard Liquid FM is a good but not great transmitting and charging solution, while Liquid FM Plus is a better deal and has the superior QuickSeek feature, but it loses the iPod Dock Connector, and you’ll have to pay more—a Monster Cable-comparable price—to get the company’s best package in Liquid FM Deluxe. We’d go with the standard Liquid FM unless you can find Deluxe at a discounted price that’s just too attractive to pass up.