Slime or air-filled tyres - worth it?

[elk4baby]

We have air-filled tyres on our buggy used to carry two heavy toddlers.
We've never had a flat tyre as of yet, so I'm not sure what one does in the situation .
I've come across something called tyre slime for bikes and pushchairs. Does anyone have any experience with this? How easy is it to 'install' and use? Does it make pumping up the tyres more difficult at all? Does it change the 'feel' in use?
If you had the choice not to, would you still fill your buggy tyres with slime?!

Given we've never had a flat or puncture, am I right to assume they're pretty rare?

[The title should say FOR] :)

We put slime in our tyres. Punctures are like buses - you may never have one, or may have 3 in 3 days. A lot does depend on where you go, and also the time of year eg hedge cutting. Its easy to put in - simply use the tool that comes with the Slime to remove the valve, squirt the Slime in and pump up the tyre again. I think it does affect performance a tiny bit but its worth it for the peace of mind.