Zmod3 is a bit of a grey area. Its useful for editing person models, but not good for nothing else. blender, older zmods (1 and 2) can create/edit vehicles, buildings and other static objects, without the 4 dollar cost.
I had zmod3 (sponsored by someone else) and it didnt give me any issues under a free avira antivirus. my theory is that the piracy checker on zm3 causes false alarms. Another issue is that there are so many many hoops to jump through when registering zm3, like how you can only use that copy of zm3 on that one computer, and if you are caught copy-pasting it elsewhere to another system, your license is blacklisted and you get a ban on site. Another issue is that you potentially have to pay up to re-license your copy if its lost in an HDD crash or your copy gets corrupted due to a glitch.
Nlender though has a bug relating to exporting which causes normals to be corrupted, but can be ignored by simply shading them over in blender before the export. It makes the models virtually uneditable though once exported, which is a good thing and a bad thing as well. Good that its incentive for people not to steal your assets, bad that once exported, editing minor bugs becomes very hard. Blender is free though, and very very powerful (for a free app) and has a lot of modifiers that make the modelling task MUCH easier than any of the zmods. Its a matter of choosing really what you feel is the lesser evil in all of this and choosing what you feel will best suit you in the long run. Zmod3 is the only one of those options that costs money, so i wholeheartedly dont recommend it to anyone with a tight budget, or no budget at all.
My general rule is not to spend any sort of money on an inconsequential hobby like em4, but often the lines get blurred when someone else offers to pay up for you. Your case is obviously different so id like to see how it pans out for you.