I have one engine on the test stand, but it is still looking for a proper exhaust.
Equipped with the 35cc pitts muffler, it turns 6200-6500 (4.5 hp) using a 22x10 Smart prop (Menz-clone, wood)
Since this exhaust is too small, and very restrictive, this realy is nothing you can go by.
Just engines's test confirm low power on their larger volume pitts-type muffler, and have shown how this baby reacts to a (wrong) 35cc tuned pipe with a 1400 rpm jump to 6.5 hp
I know that Krumscheidt is working on a dedicated pipe, and I intend to get one. What I can say now is:

Starting- after two cold choke flips, open choke, turn on ignition, then two more flips get her going. Kickback is absent.
The needles are factory set very rich. The engine, when in the box, feels rough. This totally disappeared after the first 1/2 minute run, though the engine still felt tight.
After initial coarse, and still rich adjustment, and at 1:25 mix, idle is fantastic, acceleration is crisp, mid-throttle is a smooth pace. Now my once scruffy workshop now is utter chaos, because everything blew away. At very low idle, the engine may kick back, and resume at a steady pace in the opposite direction. It has no real preference for CW or CCW rotation. Maybe for CW running at full throttle the timing is not advanced enough. I did not test, because my workbench was in the line of fire!
I have an Extra 300 of 84" span on the bench to serve as testbed. Estimated flight weight will be about 20 lbs, but the plane is a loooong way from finished.

It seems that the claimed >8 hp on a well tuned pipe is no bragging. My 50cc 9,5 hp MXracer produced less than 5hp without the pipe. Price in Europe is just short of Euro 500, so without tax That should be less than USD 500 with the current exhange rates. That is usd 62.50 per HP, by no means expensive, and very competitive both HP-wise, and as compared to ZDZ and 3W.