SSD, it is true that you can get a good view on your back (in a variety of situations, or so I am told), but (concentrating on the flying for a minute) you might miss the evil dude whilst rolling (a MK 1 Spitfire with fabric ailerons might not roll as quickly as a Yak), and anyway he would be putting some distance on whilst you do this, which is why the 109s used a pushover and hard dive to evade pursuing Spitfires. They must have been fed up when the later models with improved carburation came along and bunted straight after them.
If you are the persuer, it would be quite easy to keep them in sight while rolling - then you pull down onto the target.
I was once driving up the side of a steep valley in the Yorkshire dales when a Tornado appeared in my rear-view mirror, flashed over us, and on reaching the top of the ridge, rolled inverted and pulled over into the next valley, where he presumably continued a half-roll to erect. I'm told this is standard RAF low level technique, since it keeps the (very close!) ground in sight and also gives you first sight of any baddies waiting on the other side of the ridge.
SSD