I don't know about capacity and efficiency compared with the modern ones but for reliability I have an Ariston that I haven't had to call the engineer out once in the 10 years Iv'e had it.
Recently had to do the same thing after my old one started leaking due to rubber seals perishing to the extent that repairing / replacing them was neither practical nor cost-effective.
He disconnected the old one, John Lewis delivered the new one and took the old one away, and he connected the new one. So far, it's working perfectly, much quieter than my previous one.
The problem I found in the past with a washer dryer was that both the washer and dryer seemed to be a bit rubbish at both their jobs. Then the dryer part of mine broke, and I was left with a sub par washing machine.
Whether they've improved in the 5 year or so since I had one I dunno, but it's put me off having one again.
Agree with the others - we had one and it was a bad washing machine and a bad dryer (did have a child lock which was good). Don't know if they've improved at all. I have a large machine and it has a really good spin cycle and I do a lot of washing.
We had a washer /drier, it developed a fault, overheated and burnt the clothes in it , damn near burn the kitchen/house down as well !
I know any drier / washer can get a fault but the fire brigade said that combined washer / driers were far more likely to get faults than single units.