I'm satisfied with mine, they reputedly aid cooling somewhat also, due to the sturdy finned aluminum stock and increased surface area. But here are several warnings anyway.
Most important first: I would advise prep-ing the cover bolts and the receiving rocker-stud-collet-nuts with a tap and die. I had a cover bolt stick in the collet during removal once, and the collet nut (or the stud it was on, can't remember) was backed-out enough to leave slack between the rocker assembly and head--SEEING this was impossible, even if looking for it--and as a result one pushrod was dropped and bent. I discovered the problem only when testing the tightness of the collet with a wrench. I ended up replacing my cover bolts with shorter ones, much less turns of the wrench now, easy removal.
These covers add 'width' to the engine overall dimension, meaning that with their installation, the cramped space beside the suspenision consoles down there just gets tighter, and engine reinstallations require just that little bit more of clearance and careful jockeying on the jack.
I've had no problem with the bolts leaking, although I usually replace the rubber grommet on the bolts after a few service removals. I use an ordinary dome-faced grommet, sliced in half, one half on each bolt.
The standard factory cork gasket seals mine perfectly, with a little copper-swab sealant on the cover side, and removal is clean. The special neoprene gasket designed for these covers and sold by cb NEVER sealed for me, no matter what painstaking efforts I employed. They were made in HELL by the DEVIL.
They made cover installation infinitely more difficult (they're 'taller' than the cork gasket, meaning even less space to work) and would always buckle somewhere, usually at the top where you are trying to pry the lip of the cover in under the engine tin--they inevitably leaked and made me curse something awful.
You can vent the covers with a fitting, but you will be drilling or cutting a hole in the tin also for the hose to pass through, or utilizing the j-tube holes, if 'no heat' is 'no issue' with you.
That's all I know.
--john lambert