Franco,
As the proud owner of a variety of SOG knives I can attest that you will not be disappointed with any knife in the X-42 line(any SOG for that matter).
I own many knives including ones from Emerson, Benchmade, SOG, Gerber, Cold Steel, and Spyderco.
My left pocket carry knife is a SOG X-42 S84S Mini Auto-Clip.
My right pocket carry knife is almost always the SOG Pentagon Elite PE14. See the following link.
http://www.sogknives.com/pentagon.htm
I also own and highly recommend the following X-42's. The Titanium Nitride finish is one to behold.
SOG-T64 - Black Titanium Nitride Finish (TiNi), Plain Edge
SOG-T64S - Black Titanium Nitride Finish (TiNi), Serrated Edge
SOG-T84 - Black Titanium Nitride Finish (TiNi), Plain Edge
You specifically asked about the strength of the handle, lock, purpose, etc.
I've never had any problems with the strength of the handle. Unfortunately, one day my Mini X-42 managed to make it's way out of my pocket.
This primarily happened because the knife was sharing some pocket space with a cell phone clip and I was fishing my keys out of the pocket and dragged it out. Well, it dropped to the pavement and I stepped on it. At first, there were some bad scuffs, however, they are not noticeable now. The handle and lock are still strong. No doubt.
With respect to purpose, I've used the Mini Auto for many things including: cutting rope, cardboard, plastic wrap, plastic tie wraps, tape, coupons out of the paper, etc. etc. The steel is strong and the blade maintains it's edge.
Everytime I pull out my SOG, people ask me about it.
Get one, you'll love it. It's light, functional, and adapts to any pocket. One twist, and it adjusts.
I've lurked around Bladeforums for about one year and finally created a userid. Note my userid and you'll know my favorite knife.