I would not trust a blow-off system to any brew that's outside of it's initial stages of fermentation because of the chance of temperature pressure changes sucking back in the blowoff water. I just saw a post to this effect on this forum today actually. Could it work? Absolutely, but my feeling is that the risk is too high considering that it could be minimized for a few dollars.
I prefer to use S-lock airlocks for long term aging but there is the definite possibility of complete evaporation with these just like the 3-peice airlocks. However, I find the evaporation to be reasonably slow and the chance of suck-back to be minimal. I only fill my S-lock airlock about half as high as the 'Max Fill' line so that when all liquid is sucked back into the closest chamber to my carboy there is still plenty of headspace so that bubbles don't actually get sucked into my carboy (I hope that makes sense
). I definitely prefer the S-lock to 3-piece airlock any day.
If I knew I was planning a yearlong bulk aging on something that might be offgassing periodically, I might opt for the silicone vented stopper. So far, my long-term brews (red wines and meads) have not required more than my S-locks (which are quite cheap at about $1.25 each).