I have a system! I change it around to add another run into their setup in the winter.
I can't recommend it enough. I've had it 3 years and there's not one single problem with it - it'll last me another 10+ years. It's extremely safe - the pipe is solid so a fox can't nibble through, the doors are designed so that a fox can't fit through, etc. The fact that it's plastic means that it will last much longer than other systems on the market made of wood, and homemade versions.
We created our own connectors for one run as I was short on money. They were terrible compared to the real stuff - they kept breaking, they ended up warping due to water even though they'd been treated with cuprinol etc. Bare in mind that my stepdad is an engineer. With the runaround you're paying for safety and convenience. I can move the entire setup around the garden without having to disconnect anything. I was fed up of finding bits of the homemade one broken and having to fix it. With the runaround you just order any spares that you need.
Also, I can move their run all over the grass in the summer so they get lots of fresh grass and the grass doesn't suffer.
I'd never use anything else. It's just not worth the hassle or potential for disaster imo.