Bought one from them once years ago and it was OK- but I ran it lean and cooked it. That was my fault. TES were fine with repairing it within warranty.
I wasn't happy with Tuffnells, who couriered for them last time I used the. bloke didn't have anyone to help him unload so just pushed the engine off the back of the lorry.
remember that a lot of the problems you'll hear being caused by engines are often actually caused by poor setup. So whichever you go for, get the timing checked statically and with a strobe, get the dwell/points gap (if using points) set with a dwell meter-not a feeler gauge- and the carb set up with a CO meter, not just by ear.