if you search the forum you'll find many threads about general deadhanging.
so, on the business:
- many people (one for all jollypower.com) recommend NOT to deadhang full crimped, because it's more dangerous, due to the angles of the finger, and because it's not fully training (the angles of the fingers teamed with the thumb wrapped on to the index create a mechanical lock with bones that takes part of the effort from the tendons;
- so you should deadhang mostly half crimped with no thumb, leaving the full crimp for the bouldering waal and for few deadhanging sessions;
- also you shouldn't deadhang openhanded on EDGES because, again it's not training given that alot of the effort is sustained by the skin of those fingers that actually catch the edge of the hold. moreover, it's very common to use just three fingers, because the pinkie is too short to catch the hold with the other fingers stretched.
in my opinion (what i do):
- deadhang half crimped with no thumb;
- deadhang full crimped very little to get used to the pain and the feeling of the lock;
- deadhang openhanded on BIG FAT SLOPERS that will take the whole hand, and all the fingers, just like real slopers do.
do also some tests with different holds, find out where you're better, team it to the kind of climbing you want to do and take your conclusions.
i hope this helps.