Yes that JB weld works great for bonding PETG. I use to make my own acrylic aquariums with that stuff. Love it
About the printer, haven't heard of it and just took a look at it online. The only problem is that it has only has a 8x8 inch print volume. Which is quite small for building Armor. It can be done but you will have many more slices to do. Also, I see that the printer uses 1.75mm filament in a cartridge style which might limit your ability to choose other filament brands since the reels come in different diameters and widths.
If you are looking for a printer for building Armor I would look for one with a larger print volume. E.g. My SeeMeCNC Rostock Max V3 kit I built has almost 11.5 inch x 15 inch capability and works great for those long parts like the calves, thighs and shins. If I could get more than a 2lb roll of filament I could almost print the entire helmet on one print.
Interesting. I'm looking at it now. What do you mean by "built" and did you have to build an enclosure for it to keep the ambient conditions stable? Any tips for print speed and quality?