I bought my 75 Custom Shadow last April--I think, and had the HAJO adj.-height rear sight added on. The pistol's shot over 1000rds/month since then.
I later heard about one guys HAJO sight, that the adjustment screw broke off while shooting a match, so I bought a spare ($9) that includes the two tiny spring that will go flying when the screw breaks. I don't know if this was the first such breakage or not, but I did hear something about getting harder steel for the screw.
It happened to me this morning, also at a match

. The screw broke off right at where the screw machining stopped and the round cog-wheel head with a hex hole was cut for the adjustments. When the screw broke, the sight flips forward and the two springs went flying, but I did find the 1/4" wide head with the hex-hole. You can see right through the hex-shaped hole where the screw used to be. That hex-shape was cut all the way to touching the screw body, only
very thin steel left holding the threads to the head.
I finished that stage when the sight broke by point shooting my way to a bad score.
I did get my pistol back together with my spare parts for the next stage, and got the sights back close enough to run a steel plate-rack. Still left smiling.
I
REALLY like the sights, but I hope a stronger screw is coming.
Just giving other owners/potential buyers a heads up for "possible" problems and/or spares needed on hand. Maybe yours will hold together.
UPDATE: There is a 'new' improved screw available. If you like the CZC Competition sight, this height adjustable version is it's smarter twin brother. Life is good again.
UPDATE #2: I came in 3rd overall in the match and second on the "BUG" stage with my Sig 239. If I'd had a PO1 or CompactL, I might have moved up a notch.