I'd be careful mate. I know a sub-contracting aerial guy up here. He is straight and tells me it is very difficult to beat the "system". He has also told me a lot of horror stories about things that dodgy contractors have offered.
You will need 4 LNB outputs to run 2 Sky Plus boxes but most new dishes will have those. You will also need two viewing cards from Sky (sounds like you are being offered dodgy ones). Sky are very careful with multiroom. As has been said, it is an extra tenner a month and so Sky are concerned that unscrupulous neighbours may share a dish and have a feed through the wall so that they both get the works for less than two separate systems.
Consequently, both boxes need to be plugged into a telephone line permanently. During the night, Sky will occasionally send a request for the box to "call home". If both boxes send differing telephone information back, then you will get invoiced for two separate systems back-dated. Similarly, if both boxes are not plugged in, Sky's policy is to shoot first with an invoice.
Now it may not work like this. Maybe the engineer knows how to get round these problems. The thing with Sky though is they change things regularly to avoid fraud.
One other thing, to activate Sky+ recording facility, you have to call Sky yourself. Again, maybe there is a workround that this dodgy Engineer is aware of.
You may be paying £150 for something that works now. In 3 months time however, you may be stuck with something worthless.