Basic thing to remember about french Leaseback is that it can do ok for you if you buy the right property in the right place at the right price. Having said that, nothing on the market from any of the agencies currently meets all these criteria.
Main problem with leaseback is that it is generally grossly overpriced compared to equivalent properties in similar areas. Check the price per sq.m of the property you are buying and compare it to what second hand properties are making locally -- you will usually find that a hefty premium has been added to the leaseback project.
The other issue that keeps the bigger investors away from leaseback is the reality that it is impossible to make windfall gains on leasebacks in France. At best, the properties are valued at a multiple of the rent, and the rents are inflated annually typically against the building index or some other inflation tracker. This means that the price can not rise exponentially as can happen in free marketplace situations, so no windfall, ever.
In reality, the exit strategy from leasebacks is shaky to say the least. You will end up at the end of the lease period with a property that is worth less in real terms that what you paid for it, and with uncertain issues around the cost of maintaining common areas, pools etc. Run-down "end of life" properties like this can be hard to dispose of except at bargain basement prices.
The number of these projects coming on line at present in France is rising out of control, so be very very wary of buying these projects from here on.
Best advice on French Leasebacks? Don't touch them. In particular, never buy the so-called "aparthotel" projects where you are just buying a hotel room at a poor rate of return.