It really depends on which type you want. Some are higher in formaldehyde than others. Some you have to leave in 3 days, some you can wash out same day.
I've ordered Coppola twice from ebay. One was Coppola, the other was not. You really don't know what you'll get. Read the reviews and make sure they've been around a while, not changing names when everyone catches on that the product is not what is advertised.
On LHCF, Dream Hair is very popular right now. 2% formaldehyde though. QOD is high too, but has many happy users. Softliss is a good one, and you can wash same day. Inoar is same day wash and has a good rep. Coppola is good, if you can find it. It would be best to stick with a name brand.
The best thing about diy is you can experiment. I do mine about once a month and I get better each time. My hair is shoulder length and I use a little over an ounce and I try to keep the heat reasonable. It doesn't look all gunky when I don't wash for 3 days. It's probably not as smooth as if I had it done in a salon, but 99% better than naturally frizzy. I can do NI color the weekend before and seal it with the keratin.
Good luck picking one out. I have to decide soon whether to try something new or wait for Coppola to show back up.