I need to give the option of Panniers on Emtb´s that will be hired to Danube cruise ship guests riding on my tours.
The bikes might not have mounting holes so need a pannier system that can be clamped on seat stay/ Seat tube/ wherever possible.
I need 30 of them so not too expensive, fiddly or fragile.
Which would you recommend?

The Thule Tour XT racks would fit the bill and are proper solid once installed.

Probably not the cheapest option though.

Thule all day long. Expensive but robust.

Again not cheap but tubus do fitting kits for bikes without mountings and also you can get seat collars with mountings for the rack top mount.

I would use a tubus rack with their axle mount or frame clips and a seat post collar with mountings

Topeak do some racks called the tetra rack m1/m2 now that fit most bikes if that’s any use to you

I think it’s either Topeak or Blackburn who do a seatpost clamped trunk rack with side pannier attachments.

I like the topeak mtx system – clip bags on and off really easily without a need for faffing with elastic bits and bobs. I’d get some of them with their seatpost racks