Unless you have a specific need for HH5 because your wifi speeds are slow (and it's not your computer) or your HH3 is failing and the extra features are likely to solve your problem, I wouldn't get one not even if it's free.

From what I've read, and from two Openreach engineers who have tried them, there's a fair chance that you'll end up going back to your (say) HH3 + modem again after using a HH5 for a while.

The moral is: if it ain't broke, don't fix it. Mine isn't, so I won't.

I plugged the HH5 back in late last night and so far it seems to be behaving itself.
I do find the WiFi to be so much better compared to the HH3, even on the devices just using 2.4Ghz.

I've had to turn off 5GHz on my hub as it was interfering with my WiiU Gamepad which uses 5.2GHz.
It's no great loss as the only things I've got that can actually use 5GHz are iPhones.