I own a GTL 480 in 0.357 cal ... So - I feel I'm best suited to answer your question.
P.S: FWIW - Mine only has the Semi-Auto mode ... But you should be able to get it converted to Full-Auto (I believe Nate on AirgunChannel aka KaylaIndy might be able to point you to someone that might be able to help with that!) ... I didn't bother with the conversion - just to avoid even borderline risking any rules/ordinances with Uncle Sam.
The Good: - It's a VERY accurate gun. I'm getting about 1.5" - 2" Groups (at 55 yards) with most good quality Pellets (Predatory PolyMags/JSB/etc)
Just remember - If you're used to small bore (0.25 cal) Airguns - a 1.5" - 2" group might not sound very accurate ... But the bigger the pellet - the bigger the hole it tears on paper.
Also the more time you spend with the AG - the better you’re going to get with it ... so far - I’ve only shot maybe 50 shots (if that) ... So - with more range time - I’m sure you can shrink groups down even further!
- It's an EXTREMELY powerful gun.
I'm talking 100 - 120 FPE all day long. And that’s out of Factory. If you’re a tinkerer/tuner - I think you can easily push twice that or more !!
- You just can’t beat the semi-auto action.
Once you go Semi-Auto ... There’s NO going back!
- It's backyard friendly.
The noise you're going to hear - for the most part - is the Electronically actuator working and NOT of the guns Muzzle Blast.
The Cons: - It's trigger is NOT what you'd call match grade.
If you plan on using it for bench-rest championships - you may not like the outcome.
- It's relatively on the heavier side.
So - if you plan on carrying this around in the woods all day - you may want to reconsider your decision.
- It needs the battery re-charged every 150 shots.
So - you'll need to plan for that "downtime" in your shooting plans ... Or you could just get an extra battery or two.
- Magazines are hard to come by.
So - make sure you buy up as many as you need the first chance you see them.
- You can't really seat LONG pellets/slugs.
For example - you'll need to remove the Red Tips of em Polymags.
- They work better with Pellets v/s Slugs.
So - if you're a Slug slave - this may not be the gun for you.