Just to chip in with my experience....
I have owned a Wren 54since April 2001, the first kit was more time consuming to put together, nothing much was drilled or threaded,but it gave me a great amount of experience and understanding of how it all works.
Since, I have visited Wren during an open day last summer, whilst back in the U.k.
At this point I upgraded the combustion chamber ( with inconel vapourisers that should last a long long time), and fuel injectors, and had the engine balanced on there dynamic balancer, along with a squeeze on the tail cone it was pushing 12.5Lbs of thrust on the test stand.
A little later I upgraded to the new compressor and inlet cone, I have not checked the new thrust, but it pushes a Super Reaper vertical with no problems.
The engine has had well over 150 starts, and runs like a dream, I did replace the bearings at about 30 hrs, but that was only due to the amount of airborn sand as i fly in the desert with temps well above 45DegC, after a good clean and wash out they can certainly be used again.
This engine does everything it should and more!! Never have i had a flame out, and any hot starts have been my earlier lack of experience.
Wrens advice and commitment is second to non, great people to deal with.

Happy New Year All
Lee