If you would rather buy 20 bucks worth of ROBUX, yes.
The base amount of RBX is about the same, then a little bit with the loyalty extra, and then all the perks.
"You can't get there from here without magic, well boom I Google'd maps it." -Spose
Depends. All you really need is BC, but if you have the money and really enjoy ROBLOX, you should get it. If you do get it, preferably, get 6 months or 12 months because then OBC is cheaper.
If you're not that serious in ROBLOX, I'd say BC or TBC is a better option; OBC's privileges are more suited for people who want to develop something kinda "hardcore" with ROBLOX.