I actively support the use of these mechanics both for roleplaying sensibility and mechanic ease. I do have to engage differing descriptions of defeat may decide different body counts depending on personalities of the group but hey that is fun and allows you to characterize the hoards differently.
Yes, the mob rules are a decent way of making a group of standard 1 HD creatures an encounter that a mid-level 3E party will pay some notice too. Under RAW a couple of score goblins would have trouble even scratching many 8th-10th level characters.
I prefer the
Dungeon #113 version were mobs can have different Hit Dice. The
DMG2 one were all mobs have 30 HD doesn't seem right. A mob of 1st level aristocrat elves ought to have different HD than a mob of 3 HD standard bugbears.
Unfortunately the Mob Subtype appendix in that magazine did not include guidelines on how to determine said Hit Dice. Like 3E swarms it appears to be down to the whim of the designer (How else to explain why a centipede swarm has 9 HD but a spider swarm 2 HD despite them both being made up of Diminutive Vermin and monstrous spiders having twice the HD of monstrous centipedes).
The two examples of mobs in that Dungeon's
Foundation of Flame adventure are a 40 HD CR 9 mob of 1-HD humanoids and a 30 HD CR 8 mob of 3-HD light horses, suggesting the rule is Large Mobs have 10 times the HD of their component creatures and Medium Mobs 40 times the HD.
That would give a mob of bugbears 120 HD though, which seems WAY too much. It'd also mean a mob of 4 HD ogres would have the same 40 HD as the aforementioned elven aristocrat mob, which feels equally wonky.
If I was doing a "mob template" I'd maybe make a standard mob of Small and Medium creatures have 20 times the component creature's HD instead of 10 but add the option for Colossal mobs with twice the HD of a standard Gargantuan mob. I also like that the
Dungeon version gave the mobs a Strength boost from the base creatures and added a Str-based damage bonus to the "mob attack".