Ordo,
Personally I wouldn't go with a Rubies for a couple of reasons.
First, the size. You mentioned you have "a big head," and compared to the actual movie helmet, the Rubies is an undersized copy.
Second, if you're going to progress to doing an entire costume, once you get into it, you'll eventually see some other type of helmet that looks better overall. So you will probably want to 'upgrade.'
There are a lot of good helmet manufacturers to be found here on the board. Do some research before you buy something. For only a little more than twice the cost of that Rubies you're looking at, you can pick up a really nice resin helmet kit.
Welcome to TDH!
Eric