I'll do my best to summarize.
(discontinued). The original device which used resistors. 1 minute install, no power wire.
$81 plus shipping. Upgraded version of the original that comes with replaceable resistors to make adjustments. 1 minute install, no power wire.
$80 plus shipping. A resistor based solution that has is easily adjustable. Can tweak it in seconds if necessary. 1 minute install, no power wire.
$120 plus shipping. The most advanced solution available in my opinion. Uses electronics to adjust output, has safety functions for under/over temp, allows a remote switch disable, supports TPS idle relearn with no actions, a little longer install due to mounting and connection of one fused wire to 12V+ (battery) to provide power to the unit. 1 year warranty.
$95 plus shipping. Electronic output, overheat protection. Simple to install, but you need to connect one fused wire to 12V+ (battery) to provide power to the unit. 1 year warranty.
In my opinion, ALL of these are good solutions. I recommend VCMTunerII or S-VCM, as both of these have similar installs, but are hands off on ever adjusting the resistor, and because they show a real temperature to the ECM in an overheat situation. The VCMTuner2 costs more because it is more advanced and has more options. Both are fantastic. If I bought another one, I'd have a hard time picking between these two, but I'd probably buy the VCMTuner2.