Back when I was planning to use LiFePO4 batteries, I needed something that would support the high voltage they provided (four in series), and the 18A hobbyking ESCs only supported up to 3 cells, or around 11.1v, 14v peak. After getting advice on a hobby forum, I decided to get three of these 30A boat ESCs which supported up to 4S and had 100% reverse thrust as well. Plus, they were cheaper than the ones currently in the kits ($13 or so, and $11.50 if you wait on the page for a few minutes).
After connecting it to a motor and getting things all set up using the servo class on my arduino, I messed around with them for a while and noticed after running for about 5 minutes, the motor itself as well as the ESC would get pretty hot, then the motor would stall and the ESC would beep once a second continuously until the power was reset.
This was most likely due to overheating, considering the ESC itself has two tubes for watercooling and no heatsink fins. So, I decided to take one apart to see what needed to be cooled, and I'll end up thermal epoxying something on the resulting ICs to get better cooling than what was available before.
It looks like a simple extruded aluminum case, with openings on either end filled with silicone for waterproofing. So, I took the dremel to it and cut off either side.
Sure enough, the entire thing is filled with silicone, while the white stuff is probably thermal conducting epoxy, since it has a bit different consistency and only goes as deep as the ICs shown in the next picture.
After spending a great deal of time scraping the silicone off, this is what you're left with. Oddly enough, the heatsink is only sinking the tops of the ICs, whereas the rest of the heat is going straight into the traces of the PCB.
Overall, If you're wanting to save money, these might be a viable option, but the immense effort it took to get them apart isn't really worth it, plus the expense of extra heatsinks (unless you have some laying around) lead this to be a mediocre save of money. I would recommend everyone to just go with the default ESCs.