The style of bender you linked will work okay, but I've never been a fan of bending vertically due to the practical overhead space available for clearancing cage hoops etc. If you like that style though I would look at the One Shot from Pro Tools (www.pro-tools.com) which is setup horizontally. Like many tools, you get what you pay for and they have a nice product. If I were to recommend a bender for entry level cage building, I'd be looking at the PT 105.
Also, I highly recommend Bend Tech software. Either EZ3D or preferably Pro is great for doing cage work and really takes the guess work out, especially for a first timer. Take a look at www.2020ssi.com. You wouldn't believe how much faster and easier it is to build a cage - even I can do it and I'm no wizard.
As for bend radius (CLR or centerline radius), a 7 inch CLR is bigger than you need for a 1-3/4"x0.120 tube cage. Unless you are planning on doing thinwall bending with the same dies, you will be happier with a tighter radius (maybe 5.5-6in) for that size tube. The diameter will shrink a little in the bend area, but not much and with that thickness there shouldn't be any problem with wrinkling.