I was in London last October and went for 1 session in Diva (1 hour GBP200 + 50 extra) and 1 session with Allure (2 hours GBP500. Hurray for brexit and favorable exchange rates). Both incalls, which were easy to book. I wanted to write a full review, but it's been so long ago and the girl I've been with from Allure is not even there any more.
My experience with these agencies is exactly as mentioned in the last 2 posts: Diva provides great looking girls for an hour of fun, but if you're looking for a longer date, anything over 1 hour, in which there's some more "down time", Allure girls excel in that.
Just to say that both girls were incredibly beautiful and sex with them was fantastic, but you get different vibes from the agencies. Basically you can split the agencies to 3 categories:
1) High-class agencies, like Allure, in which the girls are specially selected and are usually exclusive to that agency.
2) Syndicated agencies, like Diva, which have hundreds of girls in the ranks, but the same girls work for several different agencies. I found the same girl I met in 5 different agencies with 5 different names. She told me it's difficult for her to keep up with the names and eventually told me her real name.
3) Fake\bait-switch\scam agencies (usually promising Japanese girls)
The price difference Allure and Diva, eventually is not that high. In most cases, the girls in Allure have "extras" included in the price (like CoF), while most girls in Diva will charge for it.