I've done periods of bottoms up pressing where I worked up to shaky singles with 32kg, and solid reps with 28kg, so I have a bit of experience with it.
Personally, I would not do any bottom up work from a kneeling, half-kneeling, or seated position (anything other than standing). IMO, two big safety factors with bottoms up work are being able to move your feet to stay under the bell, and to be able to drop it if necessary and get out of the way. I would never do something like a bottoms up get up . With a light weight it might not be particularly dangerous, and I've seen videos of people do them solidly with big weights, but I just don't see the point (plus, I don't like get ups in general).
I was at an RKC cert in 2009 when Pavel was still there, and people were fooling around with bottom up presses. At that time, I was pretty comfortable doing 24kg bottom up presses, but couldn't do 32kg, and I didn't have a 28kg at home. They had a 28 at the cert, so I decided to try it, and a bunch of other people were around me watching. My clean was shaky and it took a little stumbling around for me to get it stable. All the spectators were jumping back away from me afraid to get hit with a falling bell. But since I'd been practicing a lot with 24kg, I had a good feel for the groove, and once I got it stable in the rack I was very confident I could press it, and I did.
BTW, with bottom up presses, I consider it a failed rep if I can't bring it down under control and pause in the rack position before lowering from there.
[Edit: Also, I find that with bottoms up work, there is a bigger discrepancy between my dominant and non-dominant sides than any other exercise. When working up to new PR weight, it takes significantly longer to get it on my non-dominant side. And even after I can do it on both sides, I am much more consistent and have a better ability to save a lift that gets out of the groove on my dominant side.]
