Yeah, it would be needlessly complicated. Especially when it comes to bonuses or penalties.
I would mostly think, "Whoever designed this didn't really think this through."
Depending on how familiar someone is with different types of dice models, and how you explain it to them, it's really not that weird at all. There is at least one game that I know of which uses this sort of range band mechanic, and it is The Great War of Magellan. In order to succeed at (for example) punching a dude, you would need to roll (for example) above 7 and not above 13. While the actual math of the system could use some refinement, they actually had a pretty good reason for using this method instead of anything traditional. In short, they were taking your attack roll and your target's defense roll, and superimposing both onto the same die.
I'm sure you can imagine a system where you have a skill of 13, so you need to roll 13 or lower on a d20 in order to hit; and if your opponent gets a chance to dodge, then maybe they need to roll 7 or less in order to succeed at dodging. In GWoM, given those a numbers, a roll of 1-7 indicates that you would have hit, except they dodged; a roll between 8-13 means you hit; and a roll of 14+ means that you missed because you're not very good at fighting.
Ignoring how bad those specific numbers are, the concept is actually pretty sound. Instead of two die rolls, made by two players, each against their own target numbers; you get one die roll, by one player, compared to two target numbers.
Of course, GWoM then went off the deep end by introducing random other results that didn't correspond to skill levels. Something like, on a roll of exactly 5 you would fall prone, or on a roll of exactly 17 you hit their face and stun them for a round (these being two random numbers that are entirely unrelated to the skill level of either participant, and seemingly supersede the basic outcome of the die roll). As neat as the basic range band mechanic is, I really can't defend this part at all.
I don't think so, no. To the best of my understanding, you could have just subtracted the defender's dodge chance from the attacker's skill, and said you needed a roll of 6 or less in order to hit. The only benefits of the range band are that you can skip the subtraction step, and that the die roll gives you more information about how to narrate the resolution of the action.In that game, is there a mechanical difference between missing because the other guy dodged and just missing?
But deciding to institute a mechanic where you roll +/-5 around a single target number is no different than just saying, "Roll 10 or higher." But the latter is VASTLY easier to figure out what is needed, to apply bonuses to, etc. And it even introduces new "WTF?" flaws into things to set your range of success AROUND a target number like that. For example, if the number on the combination is "2", where do the +/-5 results fall? I mean, you can't roll 5 less than 2 on a d20, right? So if the combination number is within less than 5 of either end of the d20 scale do you wrap possible results around to the other end (so that a 18-20, and 1-6 would be your successful results)? What good is the mechanic is the combination were 50 numbers on the dial? Or only 12 numbers? It ends up being a HIGHLY specialized, situational mechanic that isn't adaptable. It may be okay for a genuine one-time thing, but even then it STILL ends up being simpler, and therefore much more likely to be conducive to flow of play, to just say, "Your target number is X, roll high." Unless the point of the use of the mechanic actually IS obfuscation.Many many years ago I did play a game session where the dice roll wasn't the simpler roll-above-a-certain-number mechanic. However, the roll requirement was a range on the die, not an random or seemingly arbitrary selection of numbers on the die. A reason (which is very important) was provided. The scenario that triggered the die roll was the cracking of a safe with a combination lock. We rolled a d20 for each digit on the lock and the range was +/- 5 of the actual combination digit. So, to crack the "8" on the first digit on the lock, we had to roll a 3-13 on a d20. I can not remember if we were told ahead of time, but I do remember that we were not trying to roll high, but roll within success range.