I was a Gravely/Ariens dealer. When I sold my shop, I made sure to take a classic LS 21 with me for my home use. Great mower all around. No, it is not made for commercial use, but it does hold up pretty well in that type of service. Hired help can tear one up in a season, but if you mostly operate it yourself, or have better than average hired help, it will last a long time. A common failure is the recoil start on the Kawasaki engine. Keep a spare recoil assy. on hand. Takes about 5 minutes to change them out. Also, height adjuster levers break off if you change cut heights a lot. Keep a set of those on hand also.
This classic model is way better in cut and overall dependability than the "Commercial" Gravely 21".
I think the Ariens 21" classic is the best performing 21" mower you can buy right now, for less than $1000.00.