Thanks for your replies, you've given me something to think about. I don't need such a high rate of fire, but if I was going to buy a TM MP5 i just thought why not get the high cycle? The thought of being excited to get my first rif and then having the internals wrecked before I even get to skirmish it isn't very appealing, though I've not seen any other people with similar stories.
Would I be better off looking at the ICS MP5 range? It seems they've been making them for years so surely must be making decent ones now. I've not really looked into them yet as was so focused on the TMs but the full metal bodies are definitely attractive