AC SSRs use triacs and DC SSRs uses MOSFETs .... One advantage of the higher current rating SSRs is if you get one rated at 100A you can ditch the heatsink for a 15A-20A heater. Frankly once you approach 20A@ 12V DC it's time to raise the voltage to 24V or go to an AC heater. Things just get too lossy, connections more problematic, etc. It's a big part of the reason I went with a 10" rather than the 12". I have my doubts about the longevity of that 12" pcb heater at 12V. Look at all the trouble they go to for the 12V high amp connections on a desktop computer with 4 parallel 12V lines to the motherboard and 2 or more in parallel to a video card