Hi,
To answer your question, I think the Metal band has a plastic bit next to the watch more for a Looks perspective than anything else.
The Adapters are made from 316 Stainless, so unless you have had a Seiko, or a Citizen watch start to rust on you in the past, you wont have any problems with these.
I cant verify the Suunto watch material, but they say it's 316 stainless, and if they are telling the truth, you wont have any issues from Dielectric corrosion either.
As long as you treat the computer as you should, as in rinse it after every dive, you shouldn't have any problems.
Other than the "Look" issue with the metal band, if they wanted to make it easy to install and not mill the ends to within really tight tolerances, a plastic edge on the last link would make it just easier to produce.
The top screws that hold the bands on are both tapered, to make them easy to insert, and also has the advantage of "Camming" them in tighter to the watch body.
The deeper the screw goes, the closer to the watch body they get.
The only issue is that someone who has never changed the band before may think that you have to remove the two screws on the BOTTOM of the watch to change the bands, but you don't.
If you loosen, or tighten the ones on the bottom, go get the waterproof-ness checked before you dive.
Get a reputable watch maker to check the integrity of the seals if you touch them at all.
If you only touch the two small T6 Torx screws on the top, it cant affect the seals of the watch at all.
I'll post a Pic here to show you which screw I mean exactly.
Also with the strap I sell, you wont need locktite on the screws, the Strap and Adapters will hold them in place without it even if you loose one screw, and when you install the screws, make sure you put them in "Snug" but not TOO Tight, they are really easy to strip.
I hope that this answers all your questions, if you have more let me know.
Cheers,
Duke