That's bad. I'm the target audience for that kind of thing. I have a job, which means I can spare five dollars more easily than I can spare five hours. The game's demographics skew young, and I don't imagine people like me are in the majority.
Why do I like it? The MTS is searchable. The in-game markets are not*. Since they take a 10% cut of anything sold in MTS, that's not surprising. Since the in-game markets aren't searchable, they tend towards higher-value items - it's not worth your time to try to find anything else. There's a lot of stuff in the MTS that wouldn't be worth buying or selling otherwise. It used to be that if I really needed an item, I'd have to spend half an hour combing the markets for it, and the moderately common items wouldn't be worth anybody's trouble to sell. Now, if I'm catching up on old quests I can just go in and buy them for a quarter or so.
The problem is that there is now an exchange rate between cash and game currency ($1 gets you between 3,000,000 and 5,000,000). That really rare item I found and sold for 2 million? Used to be totally awesome. Now it's about 50 cents worth, which isn't nearly as exciting.
This also means there are two prices for everything. It's a moderately inefficient market, and it's very tempting to spend a few hours coming up with price lists to try and make money via arbitrage (buying items cash-cheap items, selling them for game money, which I use to buy cash-expensive items, to sell for cash). The problem is that, again, I'd probably be making well under minimum wage. I don't really need another job, especially at that price.
So, will I use it? Yeah. I admit I bought some very nice equipment for our characters; most of it is going to be a part of our end-game gear, and worth a few dollars. It's too useful to ignore. But I don't like it.
*: Or, rather, it you can buy the search-the-market items for about 70 cents per search. The cheap stuff goes for 21 cents in MTS, so you can see how that goes.