I worked with a guy who swore by them I just swore at them.
But he also polished the valve stems and claimed to never have any problems.
I guess they have their place but reman builders are probably more apt to go oversize stem. Maybe.
On a 502 big block with good oil pressure, brand new valves(unpolished), and the small stock umbrella seals. After 50 hour test the exhaust side had little "gold mines" on top of guides. Not good.
Do you have a wear limit that you automatically go to a thick wall guide?
How about straightness of the liner banana shaped guides ever a problem?