You have to learn German (or French) and go onto their sites. They call a spade a spade.
Trouble is that really there is no perfect machine. If its a good all rounder its either not deep or to heavy etc.
You have to start deciding what you want to do and on what sort of ground. I have wet sand, dry sand, pasture and plough machines for my area. When I travel out of area what is the best machine for land use drops right down the list as mineralisation changes from high to low.
Get on an old really nail infested site and you can do far better with an old none motion machine than the latest computerised effort.
Give details on here of your sites and perhaps a shortlist of what detectors you are considering and people will come back with their views. Joining a club is a good way of finding out what works well (and doesn't) in your area.