This.
I use a handheld mirror and the large bathroom mirror. 2 back and sides and 7 on top. Then use a 4 to blend them together. Another trick I've mastered when doing the back/sides is to shave upwards and outwards instead of just sideways, takes the edge off.
Been doing this for many years now after getting sick of queueing for ages on a Saturday morning in the barbers and paying money for something I can do easily myself.
What is with all you people queuing at the hairdressers? You make an appointment and turn up 10mins in and out, I would never keep going to somewhere I had to queue in.