Blimey, that was my worry with halfords. Think I'll be getting it fitted professionally by someone who actually gives a sh!t about the 30k car their working on!
If you're handy, you can do it yourself in 90-120 mins for dual cams and about 45 mins for front only if hardwiring.
Tidiest way is to mount front cam on passenger side so that you can't see it from the drivers side, notch the front cap for the rear view mirror attachment to the windscreen and then feed the wires up and through the adjacent cover to the headlining, head left on the main/front cam cable and down the passenger A pillar into the fuse box. Take the rear cam wiring along the drivers side headlining and across the A-pillar then where headlining and upper drivers door seals meet, poke into the seam between B-pillar and headlining, then across the seals/headlining for rear door, poke into C-pillar headlining seam and into rear headlining trim cap. Fiddliest bit is feeding cable into rubber gaiter for tailgate wiring.
Plenty of guides about with pics, notably one on VWROC from years ago. Fitted one to my Golf R, McMaddy's GTI, the wife's A1, removed from the A1 and fitted to the Polo GTI+ that replaced it and took out my Golf's a few weeks ago - Golf now sold, Dashcam waiting for arrival of new car in a few weeks time, to refit.
With no magic box required, rear 1080p camera and heat management, I'd take a Thinkware over a Blackvue anyday. I had a Blackvue 650 2 ch for a week before it fried itself overheating over a cool week. The 2 Thinkware F770s we have between the 2 cars have worked flawlessly for about 3 years each. The night time footage is noticeably better than the Blackvue's too.