I own both the Aulos keyed tenor and the Yamaha. I prefer the sound of the Yamaha – I find it richer – but I play the Aulos more as I find it less of a stretch. The holes seem the same distance apart on both models. The only difference I can see that would explathis is that the plastic key on the Aulos is a bit longer so your little finger has less of a stretch. This tiny detail makes a big difference to me. Regarding the Thomann tenor, I bought one of these first. It sounded fine but the finish was very poor. It had rough plastic seams, it was scratched and the key screws were damaged. I sent it back and bought the Yamaha. You get what you pay for. I hope this helps.
Thanks, it does indeed!
I think I would go for the Aulos as being able to play comfortably is important. I have a low D whistle which sits in the tenor range but the lowest hole is just too much of a stretch.
You don't stop playing when you get old. You get old when you stop playing.