I've got an OS 91 Pump and use a Kavan starter. It has an honest 600 + flights and has been in several ships ; the latest a Kaos 60. I've replaced bearings twice and Hobby Services warranted a new pump several years ago. In cold off season Northeast temperatures , it would be murder starting it without electric... but I have started it by it by hand when the engine is relatively warm and primed. The instructions say use a starter so I have'nt been concerned about damaging it. I've been in this hobby awhile and have plenty of old scars from prop cuts when I flew Ukie combat , stunt, navy carrier and balloon bust back in the 60s and no longer desire getting wacked. The irony of this is that I have to hand start my DA 100 Carden Cap 232 ; something that always gives me reason to pause when I have it out.