... Blood chokes in which you reduce blood flow to the brain are more effective and relatively safe. Note I said reduced blood flow to brain, not stopping it. In reality you only cut off enough to cause them to pass out. It doesn't take much and it doesn't take long.
I practice them all the time with no ill effects whatsoever.
The way this was explained to me (by an olympic judo coach) is that we're not really cutting off the blood flow, but sort of squeezing it up into the head such that it increases the pressure on the brain, which causes blackout.
I used to do them all the time, in both roles. As long as the partner knows how to choke safely (within the tolerances for judo), you can do these things over and over with no harm.
Two caveats for anyone trying this (which I'm sure Kevin knows better than I): the partner must know how to choke without causing damage, so don't try this with just anyone or they can crush your windpipe for you; second, you shouldn't knock your partner all the way out. They should tap at the time when they can see that your choke is becoming effective and they can't escape --just before they are losing consciousness.
And one more: if you get knocked out too many times, it can cause brain damage. So don't let your partner put you out all the way. If they do, don't practice with them again.
In short, don't try this without serious instruction from someone who really knows. Get a good judo teacher to show you how it works.
Happy New Year!