Help with buying a weights set

Hi, I'm currently doing P90X and would like to buy a weights set instead of going to the gym to do the routines (and to save money of course). I've had a look around some websites and have found that this set might be best for me: http://www.argos.co.uk/static/Product/partNumber/9003156/c_1/1|category_root|Sports+and+leisure|14419152/c_2/2|14419152|Weights+and+strength+training|29022084/c_3/3|cat_29022084|Weights+and+dumbbells|14419310.htm

If the link doesn't work it includes:
6 x 1.25kg (2.75lbs)
4 x 2.5kg (5.5lbs)
6 x 5kg (11lbs)
2 x 35.5cm spinlock hollow bars with rubber sleeves.
6 x spinlock collars.
1 x 165cm spinlock bar.



As I've never used these "home" weights before I'd like to know, is it easy to change the weights during a workout or does it take too long? Can I put 2x 5kg weights on each side of the small dumbbell to make 20kg on each (eg to do 20kg curls) or can you only put 1x 5kg on the small dumbbell?

Thoughts?