what are the advantages and disadvnatages to putting hooks in vs. figure four when you have back control?
Hooks are usually easier to get, but also easier to lose. This also makes it easier to switch to armbars. Body triangle can be harder to get (though I find it easier from some angles) and is harder to escape. It can make leaving rear mount for other moves difficult. You need a good RNC to make it really worthwhile, unless you like to just hold rear mount forever but not do anything. Body triangle can also be bad for your knees. Roy Harris answers a Q&A about this on his site.
body triangle makes it easier to hold the mount (some people may tap to it if you put it on as they breath out or something its obviously pretty low % though), hooks give you more options for subs but make it easier for the opponent to escape
There are ways to apply pressure on your ankle when doing the body triangle if your on your back. It is easier to escape if you just have the hooks in while on top, so my suggestion; Body triangle on top and when your on your back hooks in.
