There are semi decent bikes, but from the sounds of it you want a bike that will be a bit more solid and be worth every penny. Lot of these bikes feature a major cost cutting component, e.g. fork or drive chain, or brakes. This means that this component will always leave you wanting more from it. These bikes all seem pretty heavy as well. If I was yo I wou
ld be investing an extra £30 or so and getting the base line Bird Zero TR. It would be an incredibly fun ride and would be nice and light for your money. OK, it would end up being maybe £50 over your budget but in reality this bike is far better than any of the bikes you have looked out. Not only do you get a fantastic ride but Birds customer service is unbelievable good. The base model TR3 is £999, but by the time you have payed postage and chosen your final spec, yes you can tweek what you want and if you are unsure the guys at bird will do a grand job at helping, your final cost will be a little bit over.
Hope this helps.