I was advised to not bother with the budget devilbiss range as they are no better than other cheaper guns and spares not readily available. I bought a kestral gravity gun for primer application and must say it seems well built and spares are available think it was about £50.
Years ago when I used to do a few scooters with celly I just used the really cheap/free suction feed guns you get with compressors.The results were pretty good, no idea what tip size they were and I used them for primer and top coat.Even now I've only used cheap ones, though I've got a devilbiss gti for when I do the outer base and clear on my beetle.
I think most of it is how you paint rather than what you use.