The Sole fitted to my folks boat was a reliable little engine, the mini 29 I think from memory, and it managed perfectly well even after we had stretched the boat from 30' to 46'. The problems we had were with the electrics and the alternator which couldn't cope with the demand from the 2 leisure batteries and starting battery and we fitted a larger unit after the original gave up! Spares were a little awkward as you are limited in where to obtain them but the distributors were usually very good about sending bits via post or carrier.
As long as you accept that these were no frills boats built down to a price rather than up to a standard then you will find them a handy and inexpensive boat. However, keep in mind that because of this the steelwork used was definitely heading towards the minimum thickness you would want.
As an aside, and I'm not convinced of the truth of this tale, but I did hear tell of a Hallmark owner who, on his first outing after taking delivery of his boat, reached the first lock and discovered that the boat didn't fit. Upon measuring it he discovered it was just over 7' wide instead of 6'10"...
Add:
Just had a look at the ebay ad, it looks like a very basic Hallmark with very little added in the way of frills inside.
Oh and having just asked... my folks boat was £14,500 when new in 1999 and I got the length wrong in the first post too, it was a 30' not 35'... Doh!