Some of the bullet ones are really good.
Unfortunately because it is the spring on the inside that matters, some of the bullet ones are just as bad as the new ones.
You can only really assess the strength by practice, I can tell how good a ball detent is going to be just by squeezing it, but that is because I have squeezed hundreds of them!!!
Sorry I cant be more helpful.
We are expecting a load of the AGD ones soon, hopefully by christmas. But then again we have been waiting since september!
EDIT TO ADD
In general yes LED and early LCD ones are good, but you have to remember they may have been recently replaced in which case it wont be suitable for a halo.