We have an 2003 8/10 javelin, and it works great. We bought it used about 4 years ago and have had no issues out of it. We run it daily and it takes all we throw at it.
Simulated process, 4/color process, spot color and everything in between. Don't let anyone scare you away from one of these machines, because it uses a v squeegee. If you have a good grasp of the fundamentals of screen printing, line counts on film, proper mesh, squeegee angle, pressure etc. you will have no problems with a used javelin.
I have ran about every brand of machine out there with few exceptions.
And in my opinion it is probably the best bang for the $$$ compared to a used M&R.
Nothing wrong with an M&R if you can get it at a great price.
As far as the software and upgrades for a javelin, they really have not changed over the years, until recently, now they have become somewhat smarter machines. The old style like mine is a tank and according to Phil at Workhorse they can get you an upgrade for an older Javilin with the new features for about 3k-5k. Not sure how far back the retro fit could go, but it is available from what Phil told me a couple months back.
There are a few other companies out there with good machines also in the used market, just make sure you go and look at whatever press and run it if you can before you buy it.
Also, make sure you have someone with some kind of expertise install it or you will have problems, no matter what brand of machine it is.
Hope this helps