Ever crack one of those things open? The pic you posted looks like the ones with nothing more than a resistor and/or diode in them. Any good tech can accomplish the same thing without the "kit" for as much money as one of those kits or cheaper.
A really common mod that does what you're looking for is often referred to as an "NPC mod" or "Negative Peak Compression" mod. It normally only involves adding a couple of simple parts and retuning the radio. It allows the low deadkey with high swing so many folks are looking for. It also doesn't result in any noticable distortion, makes the radio run cooler, and makes for a cooler amp.