Viking 150 Updates after two years and Performance to 18,000 

I get what you're saying. I don't want to feel like I'm in a plane with a vintage engine as cool as they may be lol

When you have built over a dozen and installed over 50 engine in this exact model you can generally tell if something is off. Not to mention, weight and balance was already done on this aircraft during initial installation.

They are great STOL aircraft and relatively simple to build, so I've seen.

Lets take performance / price specs with a rotax 912 for example S21 (rotax 912) useful load 500 lbs LSA Wing loading +6 - 2 850 fpm climb 38 mph dirty stall cruise speed 119 mph cockpit width 46 inches build time: 700-1000 (per rans website) total kit cost + finishing 29,000$ zenith ch750 (stol) useful load 545 lbs LSA wing loading + 6 - 3 1000 fpm lcimb 35 mph dirty stall cruise speed 100mph cockpit width 50 inches build time 400 hours total cost + finishing 35740 so I'd say fairly efficient for what you get.

They are cheap to build, proven reliable and really great slow STOL aircraft, for people that would rather go slow and have better STOL performance than go "fast" (140 knots is pretty fast for a STOL aircraft as you may know) which is what a Rans S21 is, harder to build and more expensive