One of the major drawbacks to learning at Denham (which they may not tell you !) is the distance to the training area. Because you are underneath the Heathrow zone you have to fly right out towards aylesbury on every flight before you can climb.
Not quite true - the EGLL Zone only extends to just North of Denham - we actually remain at circuit height until abeam the Chiltern NDB to ensure clearance - that's probably 1 mins flying time from the runway - then you can climb up to 2500 under the LTMA. The usual training area is within the Aylesbury - Wescott - Silverstone triangle, that's true, but students are still flying and learning on the way. In actual fact, many students find it beneficial to fly the airplane for 10 minutes before reaching the training area to begin lessons that require use of that area (or similary uncongested area) for Stalls, Tight Turns, Sideslips, PFLS etc, especially if they've been out of the seat for a week or two. Inbound back to Denham can be used for some low level nav practise or Navaid work. Many students are ready for their Skills Test within the minimum hours so I don't think the training area location is an issue.
The EGLL zone is also available for Special VFR clearances to the south which gives new students excellent RT experience, as do transiting Lutons zone to the North. Denham provides both hard and soft runway experience with both 2 & 4 seater aircraft available for training. ATC are great, the circuit is reasonably tight and flown at 750ft which means you'll get more circuits per hour than at airfields with wider circuits.
In short - well worth considering if the price is right. Do visit all the flight schools at Denham. A lot of people slate Cabair and I can't comment to their other locations, but Cabair Denham is one of the most professional, competent and well run training organisations available.
Best of luck
-S