I just thought it might have been the same build quality as the 5000 MKIIs that I use - it looks like a very similar unit. My karaoke shows usually run for 3 hours and I often use 2 of these players and they've never let me down once. But I haven't used this player before so I'll take your word for it, Adam. And I agree - they do sound a bit on the cheap side at nearl half the price of mine.
I think overheating sounds like quite a serious problem. If these units are inherently faulty then I think I'll give them a miss. But, at the same time, if it's just a case of overheating I wonder if it can be cured with a £4 internal fan fitted. I had an overheating problem with one of my powered mixers and it was cured by my electrician adding 2 of these fans. It's worked brilliantly ever since. Best £8 I ever spent!