Subal PS-30

anybody have experience with Subal's 30 degrees Prisma viewfinder (PS-30) especially for video work?

http://www.subal.com/a62c57c18/Viewfinder_amp_monitor/30_degree_viewfinder/30_degree_viewfinder.aspx

I am looking for alternatives to external monitors in order to slim down the rig and/or to limit its extensions and buoyancy.

thanks for infos!