We've had our JV5's for a while now and love it but it does have it's pros and cons. But first my two cents. Most issues with machines come down to users and suppliers not training the users correctly. I firmly believe that most lower ranged machines do not get enough training to their users. So with that in mind, you HAVE to take the time to thoroughly learn your machines. You HAVE to learn what everything does, how it affects other things. And last you HAVE TO TAKE CARE of your machines. I don't care if the manufacturer says it needs little maintenace, clean the thing every day or every other day.
Blow off dust, clean grit rollers, clean the pre and post heaters to get off adhesive, etc, etc. We equate all our machines just like expensive cars...heck even cheap cars. If you don't take care of your car like you should, then why do you think you are going to take care of an expensive machine?
But with that all aside the JV5 is very fast, very fast. You can print 14 - 4 x 8 gorgeous banners in an hour. Because it has staggered print heads, 4 of them, this means that you will really never have any issues with printheads dropping out because you have 3 other backups. Essentially you can run out of all 3 print heads and just print from the one, which is the same speed as a JV3. The JV5 also automatically replaces any heads that drop out. We have had 300 heads drop out (freak event wayyyy back in the beginning) and it still printed perfectly.
With this speed though comes a learning curve...drying time. If you have the space to let the prints roll off the machine and onto the floor then you can roll up, you are good to go. Banners you can let run on the take up reel easily but you will HAVE to get an infrared dryer if you want to use the full speed and have your prints be dry. Also, you can print these speeds on vinyl, 180, posters, etc but again if you are trying to get good color, the prints may not be 100% dry by the time they hit the take up reel OR you will have to cut your ink back a good amount, but then you lose color.
Another great point is banding or lawnmower effect. For those of you who do not know, light and dark banding or lawnmower effect is caused by your print heads. Since most machines have heads that go black yellow cyan magenta, that means that when it goes to print across the media, it lays down black first, then yellow, the cyan, then magenta. When it comes back, it lays down magenta first, then cyan, then yellow, then black. So what happens obviously is you are laying down a different pattern on the way out than you are on the way back. This is why running in uni-directional takes care of that. BUt on the JV5 the print heads are back to back on each other so in both directions it's running black, yellow, cyan, magenta...so never any banding issues.
I'm not sure if the new JV3, which has the increased speed, has the configuration or not, but you might want to check.
That's my two cents, hope it helps, but again like someone said above, if you just need to double your speed then go with another JV3. That way you always have a backup just in case and you don't spend a ton of money.
Best,