Getting a 10" dob...question on adding things to cart.

Sorry for the fuss here tonight. I have settled on the Dobs, rather than
the
adventure into Apochromats. It's the money.

Nobody has said why the Orion XT10 is worth 50 bucks more, and the
Hardin comes with Messier list and a moon filter if I remember correctly.
I'll go with the Hardin I guess. There is a barlow lense offered for 50
bucks
as an accessory. I assume this scope can handle a 300x magnification, but
the
barlow is achromatic. Would an achromatic barlow cause chromatic aberation
in a newtonian scope?

Also, there is the laser collimator. I read some literature here on star
testing, so
does this make the laser obsolete? And one more thing, bear with me
here....
is correcting the optics just a harmless excersise in trial and
error...lighly tweaking
the screws? I have read how to tell if something is wrong, and even what is
wrong, but not much on which screws to tweak. -Thanks.
Tom