I think this is being misinterpreted a little bit. This only blocks attacks that exactly equal the final number. So for their example, AC 14, and final total being 23, 15-22 still hits and 24+ still hits.
It's an interesting magic item but ultimately it's too much additional math and dice for a turn.
Looks like the roll is done at long rest, so it would be a relatively static number.
For a real short example, you roll a 10 after math, so you just put a little 10+ac misses automatically note somewhere handy until you sleep and roll again.
It's a fun little ring, and could be a really hype moment if/when it hits
So basically AC+1,except the +1 is a random slot somewhere 6 points above your AC. Yeah, I think this item would be annoying to use, and probably isn't as good as just AC+1, because your AC should be somewhere near where enemies are hitting ideally, or you shouldn't be getting attacked at all. 6 points higher might be out of their range to even hit.
My problem with it is it's a waste of a ring slot. The odds of this helping you at all are miniscule. Fighting enemies that attack within a range of <=22? This ring doesn't help you at all.
Yeah, best case scenario, It's mathematically the same as a +1 AC bump in that one more value of the d20 attack roll would be a miss than would be without it. Except the extra roll value is between 6 and 15 points above what would currently hit your AC, which is worse. If they already have to roll middling to very high in order to hit you, that 6-15 points could be higher than it's possible to roll without criting (i.e. >19)
Even assuming your AC is abysmal, like 10, if you roll a 10 on the die, you now get misses on a roll plus modifiers of 1-9 and 25 (excluding crits). If the attacker has total modifiers of 5 or less to hit, that 25 isn't doing anything at all as they either couldn't hit it or would crit to hit it. So in order to keep your extra point relevant, you would want to save a low roll, ideally a 1, for an extra point 6 points above your AC. But even that gets less useful the higher your AC is. Too high on either your AC or your roll and you have the same problem, the ring does nothing.
This ring is maximally effective the lower your AC is. And even then, best case scenario, it has the total effectiveness of a +1 to AC.A ring of protection already provides you that mathematical advantage. Plus ring of protection is less rare.
Once per long rest, when you are hit by an attack that is not a critical hit while wearing this ring, you may use your reaction to cause that attack to miss and all future attack rolls that are equal to the first roll also miss. This benefit lasts until you finish a long rest.
This is a little stronger as it comes with an automatic damage negation, but it guarantees it will see use once per day if you use it. It also negates rolling dice which consumes a deceptively long amount of time if you introduce a lot of effects that do this
Currently it seems to specify that you roll the 1d10+5 when you attune. If you know that your average enemy has a +5 to hit, the tactically smart choice is to keep re-attuning until you get a 15. However if you move that to be triggered as a reaction, then the tactical playoff is still waiting for a common value to come up but also potentially choosing to negate a dangerous hit on an attack that's unlikely to come back up like a 28 is a alternative tactical option.
The crit line seems a bit hasty. Enhanced crit ranges exist on several monsters, and that makes this magic item even less worth using. Preparing for a particularly powerful foe by bringing your uncanny AC to what you expect to be a 19 on the die is the best use I can find. However, “this does not negate natural 20s” is very fair.
The roll to hit is a single die, so if the attacker could hit or miss on a regular (1-19) roll, the best outcome is to block the lowest number, AC+6. The extra number gives no benefit against an attacker that couldn't roll that number on a (modified) ordinary roll, and gives a 5% miss chance against an attacker that could.
If the attacker has such a high chance to hit that they can roll AC+15 on a regular die, but cannot roll AC+6, you're in trouble - they'll basically never miss.
That's the most broken thing I've ever seen. Even before the "you get to keep the previous roll into perpetuity if you want" bit. Rolled a 10? Cool. You could run into battle wearing only magnets that attract weapons and arrows alike and still bounce them off your flesh like Superman.... forever.
Edit: I misread the text. My bad. No supermanning here. In fact, looks like it's a significantly worse ring of protection with a higher rarity.
Pretty sure you misread the text here. This doesn't actually give you a higher AC. It just adds one number that you also dodge on on top of your current AC.
So, in the example in the image with an AC of 14 and if you rolled a 4 you would still have an AC of 14. So if someone rolled a 16 they would hit you. If they rolled a 22, they hit. 24? That's a hit. Only the specific number of 23 would count as a miss against your AC.
The funny thing is, this item would be all but useless for a character with high AC, since you would lamost always roll over what someone was going to realistically be hitting you often with.