I have a Passier Grand Gilbert and I have to say it's my favourite saddle ever. It doesn't have huge knee blocks like the Albion SLK which I've also used but I found it incredibly comfortable and it felt very secure which allowed me to ride with much longer stirrups than I normally would. I've not tried the other models but I'm definitely a Passier fan and would have another one in a heartbeat.
Am sure that there are horses out there that have successfully used them, but the posh dressage yard here used to use them for all their horses but the saddles have now all been replaced. Also a friend had a passier for her horse and that also made her horses back sore, so she too had to get a new saddle. Have noticed that there are now many second hand passiers available on the market. I'm not sure that the way that they are made offers the horse maximum comfort.
I had a Passier and loved it I only sold it as mummy horse was sadly PTS and it didn't fit baby horse so I sadly waved it goodbye, would consider another but need a very wide gullet for him so it doesn't rest on the scar tissue from his KS Op.