does the mini spool work as good as a locker and does put to much stress on the rear end parts

Long answer:

As I understand it, a minispool is a device that basically replaces your spider gear assembly and sidegears with a solid piece.  It does the same thing as a welded spider gear assembly.

A locker is a device that has the abilitiy to lock the two axle shafts together depending on load conditions or driver selection.

A selectable locker (ARB makes the most popular aftermarket unit) allows the driver to switch from an open differential to a locked differential through extenal controls.

A Lockrite or Detroit (brand names) locker is similar to a minispool except that the spider gears are replaced with spring loaded gear facings that mesh with the existing side gears. Under load, the taper of the gear facings along with the effect of the spring loading causes the axle to "unload", "pop" or "slip a tooth" when excessive axle load is applied at the wheels.

Short answer:
 
A minispool will be harder on your drivetrain, but no harder (and probably more reliable) than welding the differential.

Hope that this helps!

That does help thanks

A mini spool is not as strong as a full spool which replaces the entire carrier.  I would get a locker if you plan to drive it on the street much at all.

My 2 cents?

Trail only?  Mini spool works fine.  Very Predictable.

Mixed Use?  ARB or other selectable locker (KAM)

Front?  ARB or other selectable?

A "Lunch Box" Locker?  Makes great paper weights.

Everyone I know who is running the Lockright locker has been more then happy with it.  I use a mini-spool in the back of my SJ and an ARB up front.  Other then a tenancy to push through corners it works like a charm.  I did finally break a rear axle though, and the other one had the splines nice and twisted.

If it is for off/on road use, I would recommend the Lockright.  But like Yankee-Tim said for trail only the mini-spool works just fine.  Just add about 3' to your turning radius. 

My 2 cents?

Trail only?  Mini spool works fine.  Very Predictable.

IMO, a lock-right is very predictable off-road as well.....one tire slips, it engages and stays engaged until the "torque" is relieved then it unlocks.......at least that how mine works.....I don't know about other peoples experiences with them.
On-road is where lock-rights tend to be quirky and jerky......I had a DD sidekick that had one in it and it would jerk the vehicle around (because it was locking and unlocking) if I was on and off the throttle a lot (this was with an auto tranny, I don't know if a manual would make it better or worse).

...............for trail only the mini-spool works just fine.  Just add about 3' to your turning radius. 

One of the reasons I decided to put a lock right in my trail only rig.