What is the weight of a BEAR BELL, a CAN OF BEAR SPRAY, a PENCIL FLARE WITH A BEAR BANGER?
Depends on the size of the can, but approximately 12- 14 oz. for all three (about a lb or just over).
Zero, 70%, and maybe about 20% depending, respectively. however - they have issues.
What is the weight of a DLASK 8.5 inch 870?
Apparently around 5 lbs, but i have to think that's high. Maybe 4 - 4.5
About 70 percent. But it has issues
Well obviously.
The dlask gun offers more than just predator defense tho of course, it's also an effective survival tool. It can fetch food, and fire bangers and signal flares/screamers that are much more effective than pen-launched systems.
The bear spray (by itself, or maybe with the pen launcher - don't waste time with the bells, if you want to do that get an air horn) is legal in many places that guns are not, and of course is much lighter and often faster to bring into play. It's also handier if an animal already has your buddy in some respects.
There is no 'right choice for all occasions". I'd buy the bear spray AND the shotgun

i'd use the tools MOST appropriate to the circumstances i was in - both if i could, shotgun if i didn't want to bother with the spray, spray if i was in a no gun area or if i were hiking long distances and every ounce counted.
Know your tools, know their limits, take with you what is appropriate for that trip. That should include firearms in some cases, and the dlask or similar is a pretty damn attractive choice for those cases.