Those £150 fixies are awful, PLEASE don’t buy one. It’s enough to put you off cycling for life. They’re heavy, feel totally ‘dead’ to ride and have utterly rubbish equipment that falls apart within weeks.
I’ve had to build up a few of these catalogue bikes in my years in bike shops, all of them from MTB to road to BMX were unbearably dreadful. A normal MTB (say a Rockhopper) took 30-40 mins to build from box to shop floor, all working sweetly. Those bikes took 2hrs or so, bending the frame back into alignment, stripping and rebuilding the hubs cos they were shite, trying to get the brakes to work.
Just. Don’t.