Everything I have seen is that using a Comma requires you to have ACC AND Lane Keep Assist.
Stock LKA really does suck and there is no way I would bother adding it to a truck that didn't come with it unless I was also adding ACC. And even then...
If I had a truck without LKA, that means it doesn't have ACC, either, as far as I know. In that case, I would just trade my truck in for one that has those things. PARTLY because when anything in any of that breaks, I would want it to be factory-installed and covered by warranty.
I have a Comma 2. I have driven about 4000 miles with it now and it is awesome. Especially since they got steer-to-zero working. I bought the C2 used, for $500 (less than $600, all in, with shipping, a wiring harness connector, and a mirror mount). $2200 for a new Comma 3 (w/wiring harness) would be a tough pill to swallow. As long as there are still used C2s out there, I'll probably stick with those.
But, can you imagine how it could go for you if you had an accident while you had a Comma hooked up to your truck and it turned out that the Comma was setup to use ACC and LKA that you installed yourself?! Even if the Comma was not engaged at the time of the accident, and even if you could PROVE that, I think an opposing attorney could still make you look very bad. "An irresponsible monster that doesn't care about the safety of other drivers."
Self driving vehicles are still a pretty new thing. I imagine there are going to be a lot of cases hitting the courts over the new few years dealing with many different aspects of how they work. And, in any case where there is any debate over whether the problem should be blamed on the driver or the autopilot device, I expect that you can count on the device manufacturer to show up with their lawyers working hard to prove that the liability is on you, the driver, not on the device at all.
