Metsman,
While tri-shot shotguns definitely have their place in airsoft I think your or anyone else's money for that matter would be better spent with a GBB as a secondary. I say this because a GBB has the ability for quick follow up shots, are easy to transition to, and can be carried easily on your person. To be completely honest with you, if funds were not an issue I would buy a secondary AEG over a GBB and keep it in your car unless you already have one. I say this because I want you to take a minute and think about how often you have used a GBB pistol as a backup to your primary if at all. Most people (at least in OH) do not use their pistol even once during the day and it ends up being useless weight slowing the player down. Now granted I'm sure our fields in Ohio are different than what is here in AZ but even within ohio we still have quite a bit of CQB and rifles can be used for contact inside the buildings. If this is not the case in AZ then forgive me and I'd say go out and buy a quality GBB like TM, KWA, etc.. But if the reason you or anyone else wants a GBB is for a backup in the field then that's fine, but I think your money will be much better spent on something you will use more frequently like a back up primary, or some quality gear, ESS Turbofans, etc.. I carried a Tokyo Marui M9 on a Serpa dropleg for about a year but ended up ditching it for the aforementioned reasons. Just food for thought.
-Jack