The mods inquestion do similar things but not the same thing...
AvgItemLevel=shows your average Item level of your gear in a nice little spot on your character pane. similar to pawn, but it uses the built in item levels of your equipment not a personally set weight/worth of the individual stats.
BonusScanner=scans the items and sums up the stats (library for other addons)
ClassLoot=tells you very nicely and quickly what the class the item is best used for (i personally use this one)
InspectEquip=opens a window when you inspect someone telling you where their equipment came from ie dropped (where), crafted, purchased (badge gear)(i Personally run this one)
Mendeleev=using the periodic table lib adds more info to the tooltip than a normal person would want... (see the addon
page for more info
Pawn=allows you to assign weights to the stats giving gear a single worth (I use this one also) Really worthwhile for quickly comparing 2 pieces of gear.
Like I said similar things, they all add info to the tool tip or screen giving the user more info is good, but too much can create confusion. if you have pawn set up correctly, then I would keep that one and drop avgItemLevel, I personally would probably run both classloot and mendeleev (they both add a lot of info in different ways, but I run other addons that tell me what mendeleev tells me). As for inspect equip, i run it cause i am sometimes curious where that awesome looking item is from and don't feel like asking the toon who is sporting it. (also allows me to quickly see if someone's wearing gear from ulduar versus naxx without having to know what the item lvls of that gear is. Bonusscanner is a library or originally was (now it is it's own mod if you use the continued version). Use it if you need, but some of your mods may require it.