I've seen some dodgy results using polybond to seal plaster on walls and I stay well clear of it.
I get my paint in the trade centre in Fleetwood along by luas line down near the canal - get a couple of 17.5 litre buckets of their white matt emulsion and slap it on. You won't believe the cover that paint has. Two coats of that and then go round and do your filling, sand it when its dry and then put on two coats of your finishing paint. You'll get a quality finish that'll last for years. Personally I think any other way is a shortcut and won't look or last as well. From the 3 months I spent working with a painter I've a simple rule - if he wouldve done it it was a shortcut - so I always stick on an extra coat when in doubt as you'll be wanting the best possible finish in your own home.
If you can pass off looking like a tradesman give a trade centre a go, if you are gonna look like a clueless DIY head it might be embarassing and they'll charge you the full whack, but if you can get hold of that fleetwood emulsion do, cos even without trade discount its a decent price and great paint.