The sound is great.
My main issue with this engine is the 20:1 petrol mix, which is very different to any other petrol engine.
This require to cart another fuel container to the field if you have multiple petrol engines powered aeroplanes in your fleet.
It also spits a lot of the oil on the aeroplane, which is what you try to avoid by using petrol powered aeroplanes (compared to glow).

I had many issues with the engine after it was involved in a crash early on, so it is hard for me to give unbiased opinion.
When it works, it is fantastic little engine.

Eran