The full size wheel robs you of boot space, the floor is around 50mm higher than previously, and as Anchor man has found you can see the underneath of the boot floor.
I noticed no difference in the handling ride or anything else as far as driving the car, in fact it may have improved the handling by the extra weight at the rear, same with the towbar, i noticed no difference to handling.
The two combined add a huge weight of around 27kg for the spare, and around 21kg for the towbar, so around 48kg added to the back of the car. Something to consider, but as i've said i drove the car new with both not fitted but added later.
On the mazda247 forum someone estimated that a spare cost 0.1mpg of fuel.
Space savers for my use are pretty useless and really only for emergency use to the nearest garage, even if my son had one the speed restriction of 50mph? would have added lots of time to his normally 2.5 hour trip, although he got the puncture half way down.