I am very pleased with my Littermaid Mega.  The advice XMar provided will be
very helpful should you decide to get this particular brand.  Like you, I
have two cats, so I thought I would share some information about my
experiences with the box.
I try to empty the receptacle about twice a week.  At first I would empty it
daily, but I soon realized that wasn't really necessary.  I also completely
replace the litter in the tray at least once a week.  Your maintenance needs
could be completely different from mine, of course.

I don't know that the device reduces labor significantly, it seems to me
that it does, but its main appeal to me is that it controls odor
magnificently.  People visit my home and remark that it doesn't smell like
two cats would be living there (and I live in a small space).

Good luck and be sure to let us know how it turns out.

Best Regards,
Catherine

What are the top 2 brands of litter do you find best to use with it?

Thanks,
Debbie

I dont know about others, but I havent had a need to maintain mine very
often. I have heard people cleaning off the sensors or totally replacing
the litter etc. I have done neither with mine for I havent had the need....

I do occationally wipe it down but I dont put much fuss into mine.

  I *suspect* (but don't know for a certainty) that

Our store around here has "Odor Lockers" but I have not heard of
"Litter locker".  Could it be the same?  I was going to try some of
that next.  I don't like the smell of the clay litters, even when it's
99% dust free.  I have tried both Swheat and World's best.  And they
are good, a bit more spendy.

How deep should you have the litter in the box.  I usually put the
whole box in so it's about 4" deep.

Thanks,
Debbie

Rubbish!  I have 2 LitterMaids, 1 Purrforma (modified by me), and a regular old
cat box in use.  Most of the LitterMaids have been in use for 1-2 years or
more, and the Performa for slightly less than a year, and have never had an
injury to any of my cats.  

The LitterMaid has a "crash bar" on the return side of the rake mechanism that
reverses direction if it comes in contact with an object, while the Purrforma
lacks this feature (though it's slower speed rake might make up for it in some
way)  Neither one will stop the rake via IR sensor. (I could be wrong, but they
don't claim to, and in my test - using a book, they didn't. I think that should
be a standard safety feature.)

None of the automatic boxes have suffered from motor burnout, but one
LitterMaid broke the flexible motor wire, which spools out with the rake.

If the LitterMaid boxes have failings, I'd list them as:
1.  The rake is difficult to remove & clean (not really meant to be removed)
2.  They are a bit noisier than the Purrforma, though they rake faster.
3.  The motor wire is a weak point in the design.

..As for the Purrforma...Whoofff!...
1.  The stock rake is too vertical, and at the end of its sweep, isn't even far
enough over the tray to completely push the poop into it - some just sits there
on the edge of the tray obstructing the tray lid.
2.  The tray lid actually hits the outside cover of the box before it is
completely open, binding on it and dogging the motor. (Did these people
actually try their own product?)
3.  The motor is under powered.  Before I modified the box I have, the rake
would actually stop just trying to get up the ramp by itself, let alone try to
push a poop up too!
4.  Poor fit of the outside cover.  The locking slides on each side don't even
slide far enough into the cover to lock it - another case of "did they even
look at their own product?"
5.  After a short period of use, the rake starts to bind on the metal guides it
is supposed to slide in.

..Mods I did to my Purrforma to make it work better (if you didn't get your
money back already)...
1.  Bend the teeth of the rake towards the poop tray so that they all protrude
about 1/8" to 1/4" past the edge when the rake is at the end of its travel.
2.  Use some grease on the vertical slides that the rake goes up and down in-
it'll make life much easier on you and the motor. (I even put a little grease
along the length of the plastic ridge the rake slides on.)
3.  Mark the sides of the outside cover (not the tray lid) where the tray lid
first makes contact with it, and with a utility knife CAREFULLY trim off the
vertical plastic molding from there to the end, leaving just the flat,
horizontal surface.  It'll reduce the binding quite a bit, and give the motor a
bit more power!