Sounds like you just want a flash and go generic map. May as we'll give them a try, if your not prepared to travel to a known reputable dealer then your probably not bothered about figures or a health check on your vehicle?
The advice anyone will say is stick to a reputable dealer recommended by the guys on the forum. If you have searched and not found anything then they probably aren't specialist and known on the "scene" it's definitely a risk. . .
It's your car so it's up to you, I'd rather pay a bit more fuel and know my car is in safe hands and I'm getting decent aftersales care to go with it
If you do go there, let the rest of us know the result