I think freerolls do have some merit, though I have stopped playing the $10 freerolls where I can only win 50 cents (a big investment in time for too little value).
There are a lot of all-ins early in freerolls, but this is actually good practice for teaching patience. Yes there will be lots of suckouts and when 6 people are seeing a flop, you have to assume that someone always catches something. Micro-stakes online is very similar because folks playing for $1.00 have a lot of the same tendencies. Either way, it is always good to know how to play against any table dynamic that comes your way, whether it be live or online, free or not.
The allin folks in freerolls, are using different logic than aggressive bluffers, but the result to you is the same - do I call or do I fold? The logic of an allin freeroller is that he is just hoping to hit a flop or two and double or triple up. The logic of an aggressive bluffer is to get you to fold the best hand. Either way you are faced with the same decision (call/fold), so any practice working through this is good.