Quoted:
personally, i like the new 'M4-style' stock like the RRA better for the longer drop from heel to toe (more like the fixed stock so it shoulders better). the new 6pos gets you out to A2 length in the adjustments and everything in between. oh yeah, it's MUCH cheaper.
scott out
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I will agree those newer ones are nice because they are more of a full height stock. But, everyone should know that there is absolutely nothing M4 about them. That's just something someone decided to call it to sell more of them.
As far as # of positions goes I have only ever used 2, full and collapsed. The others were just "there". 6 positions would be nice to have if you ever needed it, though unlikely. But better to have and not need, I guess.
My advice is to find one that looks to be good quality and the price is right. Plastic stock and metal buffer are a must. I think I bought mine for about $40 at a gunshow about 2 years ago and have not had so much as a problem with it. I might have even gotten a card from him but I can't remember. I will post his info if I find it.
Otherwise as was said the 6 pos. RRA are supposed to be good and affordable.