I have many guns but since I got my SR9c, I have not carried anything else. To me, the best feeling best shooting handgun I own. Put over 1500 rounds through it with no issues. The SR40 is the same gun just a little more muzzle flip.
The SR40 should be a good gun but I haven't fired one yet so can't say first hand.
My son in law and I were comparing his SR9 and my Glock 23 and both are pretty darn good. No reason to expect the SR40 wouldn't be good, as most Rugers are.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together. You'll remember the quality of a gun long after you forget how much you paid for it.
US Army 1966-69, VFW Life Member, Retired Geek