frustrated by UK pipe thread

Thanks for looking at this. My wife liked this shower diverter from Hudson Reed - http://bit.ly/1gm3Nhj - didn't realize it was a UK company at first, since it was a US distributor, but it's caused a problem. First off, the thermostatic mixer/diverter didn't come with US adapters. Called the company, and they sent those from the UK. But the adapters just wind all the way into the unit - they're straight, not tighting, so there's nothing really to hold them tight. Even with teflon tape and threadlock, the joins start to drip after a few minutes. My plumber basically thinks this is just garbage and wants me to send it back and buy American. I'm about to do that, but before I do, I wanted to see if there was something easy he was missing. Is there supposed to be a gasket or something that works with UK pipes to make a proper seal? They can't possible expect lasting installation with non-clinching pipes and teflon tape?!?

I had this problem with a UK tub and shower faucet that a friend had purchased on ebay. The only thing I could do was to solder the connections. Luckily, the threads were brass and the adapters were copper. Worked out well, but I advised my friend to stop buying foreign faucets. They just arent worth the hassle.