Depends on how you plan on using it. I don't have the Vax bass, but do have the El Cheapo Vax 300 guitar. Surprisingly accurate on some of the models, not so much on others. For high $$$ studio work for others, I'd rent a pile of guitars if I didn't have at least a couple good guitars to haul in. For your own studio stuff, band demos, writing your own, etc, I wouldn't hesitate to use the Vax.
In fact, I've found some of the models to be downright inspiring since they force me to think a little differently about some material I don't own the 'real thing' for. They also allow me to try out different instruments with a flick of the switch, far faster than inspiration can leave you sometimes on the fly. Even hitting the wrong instrument can result in the occasional 'Whoa, never though about that one before' moment.
If you already have a good go-to bass and are looking for something different without laying out big bucks and the Vax can be had for a good price, snag one up. They don't depreciate below a good sale price so it's not like you'll lose much if anything on the trial. I wouldn't make it mo one and only, but it doesn't sound like that's what you're looking for. Keep in mind most people who keep Variax guitars change out the necks and love them. They're an easy swap with Fender necks and aftermarket replacements.
I don't know if the Workbench software works on the basses, but it does wonders for the guitar. Makes it extremely tweakable in ways you can't even imagine until you try it out. Even the owner's manual for the SW says you might find things by making combinations that the factory never thought of. I know I already have, at least things that aren't documented anywhere I can find.
In the end, let your own ears be the judge, not board posters who don't even know you.
It felt cheap to me (esp. feel wise), next to my Music Man Sterling, and HEAVY...I sold mine off. I will admit, I had fun with the 12-string and upright sounds, since they were such a change in sound. As another poster said, some of the models sound more authentic than others. The Stingray model sounded one of the furthest... NOTHING like a Stingray, and having owned one previously, I could really tell.
I don't know how you were planning on purchasing it (since you may have to buy it online), but definitely make sure you play it first.
I was fortunate enough to play mine before buying it, but still decided to sell it...
I have one. I use it when some band comes to record and brings a lousy bass. I run it through a Tech 21 Bass Driver and get a more than decent sound. It's not excellent, but well worth the price, IMHO.