One wag on FI once said "If you can fog a mirror, you can pass FLX training". I'm not sure it's that easy, but I didn't think that the groundschool was terribly difficult. It's not studying for an FAA written, but it's not astronaught training either. Austin definitely knows his stuff, but he doesn't go out of his way to make it hard on you. That said, it seems like they're having about a 50% pass rate lately. This may be due to the cattle call approach to hiring. Basically, call Gary (Recruiter, defacto assistant DO), if you have the times and you don't go out of your way to show that you're a jerk on the phone, you'll be given a date to show up for training.
The 210 is a nice flying airplane, and I don't think they're doing the sim anymore, so I would concentrate on being ready for groundschool. Download all of Austin's "very easy guides" (see link above). I had the most trouble with 135 duty/flight time limitations and the 135 departure/alternate mins. YMMV.
As far as the job, it's good, if you know what you're getting in to. If it's legal, you're going. If you want to make "a lot" of money (~35k, before taxes), you're going to be at work a lot. You'll get used to sleeping in recliners. On the long runs, it's basically get up, go to work, come home, eat, sleep, repeat. Getting days off is extremely tough. If you plan on having a long run, you might want to to renew your medical, register your car, get your driver's license renewed, etc etc BEFORE you show up for training.
All of that aside, the company treats you well. There's no pushing to fly with broken airplanes, and if the weather really is too bad to go, you won't get pushed there either. If you show up for work and do a decent job, the DO will try to accomodate you as much as is possible. There's definitely nothing shady or underhanded about the operation. Just a lot of work, but a lot of fun, too.