Bob, Have a 20 ga DT ejector skeet 21; it is the grail in grouse/WC cover. Mostly shot 12 and 20 ga SST guns. The 21 SST is good, not perfect, and better than many others. BTFE, yes, for a mostly target gun. Never saw any difference in my scores straight vs PG.....shot my first 100 with a 26" 12 ga straight grip.
Field. Back in the '80s-'90s took truckloads of scratch birds with them. Most 21 skeets are game gun fast, if heavy. The heavy part is not so much a liability IMO. In my hands sub-6#ers are nice to carry, not so nice to make hits with. And on a windy day would much rather have a tight-choked M-12.
Have used 21s with pads and w/checkered butts. The only buttplate I did not like was a steel skeleton. Too much slippage, range or field.
Prefer a solid rib for a mostly field 21. My VR 20 feels like a tank, but maybe that's what you want in a dedicated range gun.
Never owned a 21 Trap, but shot a couple. They are simply wonderful.
JMO, but LOP is the most over-fretted stock dimension. Have done just fine with 13.5" to 14.75" skeets (am 5'9").
Can't answer the chokes question without knowing intended use. Will say a 12/16/20 WS2 works on birds to a full 40 yds assuming premium shells.
26" bbls are not what I'd want for NSCA, but still work well on a skeet range.
