Blueprint is only
£130I assume they will be charging £100 to fit it, the £150 part will be worth max £50 (probably less) and they will oversell the fitting to make it worthwhile, the £350 part will probably be direct from Mazda, if your Mazda is anything like my local one they keep a limited supply of parts on the shelf and order on demand, so it likely is a special order for them, they also charge over the odds because its a Mazda (next time don't buy Mazda).
I would fit Blueprint, also, if you call around various mobile mechanics they will be cheaper as they have less overheads, the average cost of labour is around £50+vat where i live, the high end can be £60-65+vat, the lad i use is £25+vat, and don't think because someone is cheap they won't be anygood, you can take your car to main dealer with a basic sensor fault, they will whack it on a a fault finder and could replace 5 other parts before they replace the sensor, the lad i use i call him up and he is spot on everytime, no messing around.