I spent a lot of years using Inon stacked macro lenses and an Inon WA on my Oly 5060. You get used to the weight and small hassle of carrying them around and screwing them on an off (I had the 67mm thread versions). It does offe great flexibility to be able to potentially shoot whatever comes up on a dive. The previous comments about missing a shot by trying to madly put on whatever lens is desired are correct. You will absolutely insure that as you are putting on the wide angle for the manta, something small and once-in-a-lifetime will pop directly in front of you.
Having said that, i graduated to an Oly E-PL2 and have decided that the best all around set up for me is to use the stock 14-42 lens behind a Zen dome port. That gives me a true 28mm (equivalent) wide angle to 84mm zoom. By adding the Oly 67mm threaded holder with one or two Inon macro lenses, I can very quickly do almost anything since the holder just snaps on and off very quickly. It's almost the best of all worlds for the way i shoot. If i know I am going to be on a wreck or in a forest of soft coral, i put the 9-18 behind the zoom and go only wide angle. If i am night diving and overloading on macro subjects, I put the 14-42 behind the Oly flat port to get the extra 30% or so magnification, and then stack the Inon lenses on top of that.
Anyway, I would recommend the add on lenses for your rig, they give you more options for sure. Good luck!
Having said that, i graduated to an Oly E-PL2 and have decided that the best all around set up for me is to use the stock 14-42 lens behind a Zen dome port. That gives me a true 28mm (equivalent) wide angle to 84mm zoom. By adding the Oly 67mm threaded holder with one or two Inon macro lenses, I can very quickly do almost anything since the holder just snaps on and off very quickly. It's almost the best of all worlds for the way i shoot. If i know I am going to be on a wreck or in a forest of soft coral, i put the 9-18 behind the zoom and go only wide angle. If i am night diving and overloading on macro subjects, I put the 14-42 behind the Oly flat port to get the extra 30% or so magnification, and then stack the Inon lenses on top of that.
Anyway, I would recommend the add on lenses for your rig, they give you more options for sure. Good luck!