I have used one coat plaster once, can go over many surfaces and is very versitile, all is needed is one coat of PVA at 3-1. Its a mixture of a backing plaster and finishing in one - hence the name, but it reality it still needs to applied in two coats. Its got a three hour set so you have loads of time with it. apply the first coat and trowel it as normal. Leave to dry and then adding a second thinner coat, darby off and fill voids and repeat. On average you need to wait about 25 minutes and then this is where the sponge float comes into its own. Splashing water on the wall and using a sponge float rubbing in circular motions you will see a slurry (fat) come to the surface you then move on as the rubbing is over. Sponge about a third of the wall at a time. After you rub up go back to the top left and with a trowel and a brush, splash water and trowel over (as one coat loves water). Wait about 30 mins and then trowel entire wall. You need to go back and repeat again.
But in saying all that I prefer multi finish......