I have a Jiffy J-1. Definitely worth having.
Make sure you only use distilled water or you will end up having to clean the mineral deposits out of it.
I bought a used J-4000H that I have since sold. It is the one where the water is put inside the machine in an inner tank, as opposed to having a bottle outside and only a small reservoir. Anyway, the first time I filled it up I took it outside to empty out, you know, to give it a rinse. What came out was 50 years of white calcium powder! I rinsed it out ten times before the white chips and goop stopped pouring out.
I've only used the J1; however, the pro model gives you more versatility if you think you might use the steamer for more than just hats. If you're just steaming hats, it's hard to see anyone needing more than the J1.