I think the Tokina is a great lens and I bought one for someday just in case I wanted it. But the WWL has some advanatges. It is a very sharp lens and affords a semi-fisheye FOV that is pretty darn sharp corner to corner and is zoom through. Additionally it can be removed and on another dive, the same day, shoot flat port or macro without opening the housing to change lenses and ports. As to size, weight and bouyancy, yes it is a large chunk of GLASS and metal. The foam float collar on the WWL-1 and the new metal collar on the WWL-1B negates any negative buoyancy issue, it is approximately neutral. My Nauticam NA6400 balances neutral and in the vertical plane perfectly. My dome port and 16mm pancake tends to float dome up and the rig is slightly bouyant so I need to add ballast with it.
There is also the WWl-1C (Compact) which does work just fine with M4:3 and APS-C cameras and is more compact and lighter and also has a built in float collar and is zoom through also. If it had been available at the time I might have chosen it. Supposedly not quite as sharp, I doubt anyone but the most persnickety pro would know. But it will be in the extreme corners where there is a difference.
With any wet lens, especially if jumping in with the camera, you will need to burp and fan it. It takes me about 20 seconds with the bayonet release to burp, fan it and the port glass and then click it back on.
Since the WWL-1 is slightly negative, just in case I get distracted and for some reason jettison the lens by accident, the WWL is always tethered to the housing and the housing is always tethered to me. And the dome cover is either tethered to me or to the WWL.