Wally, let me know how you like the Zero. Just sold my standard Hellcat and bought the OSP. Was thinking of going with the Zero also but can’t decide.
I just got back from the range with its first outing. Didn't have the optic screws mounted tightly enough initially, but no issues after re-tightening them. I used the iron sights do a pre-shooting zero but not knowing the Hellcat sight picture, turned out it was about 4" high at ~10 yards. Tweaked it and then ran ~130 rounds of 147gr FMJ, 50 rounds of Brown Bear 115 gr FMJ, and finally 50 rounds of my carry ammo 147gr Winchester Ranger-T JHP. No failures of any kind. So initial experience was very positive. Off a sandbag at 10 yards there was not enough difference among the three ammo types to attempt further tweaking of the zero.
Shooting at our club's steel 2/3 IPSC silhouette with 4" pivoting center plate, in rapid fire I was hitting the pivoting plate about 75% with either optic or the laser (which was not so rapid as it was hard to see), the misses were all on the left side of the opening. Looks like I need more time with its trigger, some dry fire is in order, the laser is a good aid for this at home.
What I don't like about the Romeo Zero is:
(1) you have to remove the sight to replace the battery.
(2) the adjustments are non-click and need an 0.050" hex wrench to adjust.
What I really like is the size, weight, and price -- Joe Bob Outfitters had them on sale for $150, mine came last week so they may still have some.
The laser sight wandered a lot during the first ~75 rounds I kept tightening the screws and re-adjusting (to the Red Dot) after four times tightening, it stabilized and no further adjustments were needed. Day was too bright to do much more with the laser than get the zero stabilized. Part of it may have been the filing I had to do to get it to fit the Hellcat rail. If it doesn't stay stable I'll get the one with the coupon than came with the pistol and move this laser to a different pistol.
Its always a problem with mounting parts made of plastic its hard to know when the metal screws are tight enough to hold but not risk breaking it. So needing tightening in the first outing is not necessarily a bad thing. A few more outings should build the required confidence to start actually carrying it.