So far, I've experienced two.
I bought, for £135 (approx. $210) thw Fretless Electro-Acoustic 5 string, last year. Took a while to arrive, as I think they were on the boat from China when I ordered it from Thomann. Turned up - needed a setup, of course, but - for that price - who could complain, eh! Well... me.
After adjusting the truss rod (neck pocket) and sticking some decent strings on it, I noticed that I couldn't get rid of a buzz on the E, A and D strings, roughly around 2nd-3rd fret. On close inspection, I found that there was a 'scalloped depression' at that spot; possibly as a result of the truss rod not extending all the way to the headstock. I've known/heard about that problem before, with neck-pocket truss rods. Also, there was an odd looking, filled-in hole over the neck pocket... looked like it had be drilled and filled. After a few frustrating days of trying to decide whether or not to attempt my first fretless fingerboard sanding - I decided simply to send it back. Thankfully, Thomann were kind enough to accept the return, no fuss. Shame - apart from that suspiciously fundamental flaw... for that price, it could have been a good cheap bass to fettle and tweak. It was an all laminate body, so, given the lack of quality on the fretboard, I doubt the body would have endured years of playing/transport/gigging. I was rather disappointed.
Other end of the scale... a friend of mine, in a band called Funkasaw, has always been one of my favourite bassists; he's f'n awesome. Used to listen to him when I was a kid; the guy can make anything sing. Or growl. Or pound. Or sound as slick as silk ice. Went to hear them at a battle of the bands (The Diamond, Sutton-in-Ashfield) and he had what at first appeared to be a Fender/Squier Jazz 5. So I asked him about it, had a look. Harley-Benton Jazz copy 5. I was a bit surprised, given my own experience with HB. He'd replaced the stock pickups with Seymour Duncans, set it up properly, and whacked new strings on it... he sounded... well, as he does. AWESOME.
So, I think, as long as you can modify a bass/have a decent tech who can, their copy models are very useful at an incredibly low price; however, do not expect actual quality. Having said that - I'd like to find out, in 10 year's time, if anyone who bought one still has it in good condition.
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