I have 2, a 10 gauge R model (finished equivalent to an R-10, but old enough that I don't think it was then described as such)with 27-1/2 inch barrels and a 12 gauge P model finished to grade 19 with 30 inch barrels. Both are lovely guns, although the 12 gauge trigger pull is a bit heavy and not really adjustable (both Kirk Merrington and Geoffrey Gournet have looked at the issue and said they wouldn't touch it and JJ Perodeau passed without looking at the gun after hearing Kirk and Geoffrey had tried without success), so I would recommend having a trigger pull gauge with you in addition to the other measuring tools. Both had adult sized stocks (14 inches plus) and relatively little drop, which meant I could shoot them without changing my shooting style.

I have looked extensively for a long barreled 28 gauge, but have not located any that were within my price range.

16 gauge guns with short barrels (25-1/2 inches) seem to predominate and many have stocks with lots of drop. The recommendation that you handle and, if possible, shoot one before purchasing is well worth considering.

For the level of fit and finish, a higher quality Darne, particularly from the pre-WWII period will match (or sometimes better) a similar grade British gun from the same period and generally prove to be more robust, but at a fairly steep discount in price.

Go for it.