So I just looked it up and it looks like they have raised some of the prices since I purchased the boundaries. Everything is a one-time purchase which is the advantage over Gaia. In order to purchase the overlay maps you must get the pro upgrade which is $11.99. Available Add-Ons for CO include land boundaries ($9.99) and GMU boundaries ($11.99). onXmaps looks like a really nice and fairly easy to use interface, however judging from pictures there are some features that I use a lot BN, most specifically USFS maps. Fair disclosure: I am a software engineer and for the most part am willing to sacrifice form for function and ease of use for flexibility. BN also has lake contours for some states (CT, MN, WI, WA, MI, MT, NH, ND, and OK) and some other random overlays.
As far as OTC elk, no specific units to avoid that I know of. I would target areas bordering the limited draw areas and if you have to go early in the season I would target the higher altitudes to try and get into the rut. I hunt between 7500 and 8000 (unit 131) and they are usually just starting to heard up for muzzleloader (week 3).