I bought it as it was cheap, but the processes were different to what we all associate with BIR so haven't made anything 
That's not to say the results don't taste good though 
W
Thirty years ago I'd have bought this without thinking!
I'm not one to put something down until I've tried it - but I've already been down the onion puree road many years ago and it didn't lead to a very pleasant place (for me, anyway).
Not to say that there's no place for it; indeed, many traditional Indian dishes call for either a boiled or fried onion paste (some require both), but this will just be part of a recipe that produces a curry with a gravy (either yogurt based, for the likes of korma and pasanda, or tomato based, for basic lamb and chicken curries).
Still, as you say, Whandsy, it's cheap (77p for the Kindle version), so worth checking out.
Let us know how you get on with it. Often useful gems of information can come when you least expect them.