OPV on DSMB ?

[Centrals]

There is self-sealed open bottom smb available eg. Buddy. I never had any problem on losing air on the surface. The unit also comes with an opv.

 

[OkByMe]

I have OMS SMB and lift bags - all are open bottom with a check valve to prevent spillage, an OPV to prevent over inflation and the straps sewn all along the seams to reinforce them. All of them will inflate and stay tight out of the water. The open bottom and skirt allows the bag to be inflated simply by putting a regulator under the skirt and pushing the purge button. They will stand tight from as little as 25 feet. I had a closed bottom one once and it had to be inflated with a nozzle or a spare low pressure hose. I popped it adding its lift to a bag one day and it did not have an OPV.