A £150 map wont be great, will be a generic file probably. But does that make it bad?
I would prefer a generic file that has had lots of development and testing that a custom map made by someone that doesn't have a clue. Anyone can buy an OBD interface like KWP2000 from ebay and use a hacked copy of WinOls and claim to make custom maps.
Firstly work out what you are getting for your money, is this a genuine custom map based on datalogging and dyno testing, by a software engineer that has plenty of years experience with your car and engine, or a custom map based on plug in a laptop and hope for the best?
Custom means nothing these days, everyone claims to be making custom maps, I have seen 'custom' maps that only have 2 maps altered by block percentages so work just like a plug in tuning box.