We bought a 2nd hand 60L Engel about 7yrs ago and a 2nd hand MSA drop slide not long after, fits very nicely on the drawers even with a cargo barrier and is very functional, people are always commenting how much they like the setup.....and for us it's definitely been one of the best mods we've done!
As good as it is though, there are some drawbacks and probably worth mentioning even if it seems obvious:
1) The drop-slide is very heavy at 36kg, and together with a loaded fridge it can be difficult to operate if you're not confident or lacking strength. Especially if the car is lifted....just ask my wife
2) The fridge slide needs to be fixed to the drawers so unless you move it across and lose even more room, the mounted drop-slide will prevent quick access to the wing area. We have our compressor and receiver mounted in there along with some electrics so not a real issue, but I did once or twice have the air-fitting jam open and it was a pain to remedy without access to the wing area.
3) You lose quite a bit of room in the back of the wagon, so we made some plywood lids for the drawers which pack nicely either on or alongside the fridge.
4) Not sure about others but our MSA behaves differently depending on the weight of the packed fridge so if you start with it fully packed, it 'drops' quite easily and if you're not ready for it the potential to catch you or your fingers with a nasty pinch is always a worry (mainly) for people not familiar with it. Once it becomes lighter / emptier, it can take a bit of force to make it 'drop'....not a problem if you're familiar with it but can be a hazard if you're not expecting such resistance and then suddenly it goes.
5) Getting the drop-slide out when you need the space / flat surface can be a pain so we used some 316SS captivated-nuts to make it easier removing and installing the slide - it helps a lot!