That filter looks like it might be in a plastic housing, which would not be the most durable thing.
I have one of the Bintel ND "Moon" filters and it is quite effective, the cost is the same as the one at Aus Geo as well so the only difference might be postal cost.
http://www.bintel.com.au/Accessories...oductview.aspx
The Celestron one is also a green filter rather than ND so it will introduce a colour cast where the Bintel one is quite neutral in use. I am not sure I would like the green on the moon myself but that is a personal choice..
In the SCT (the 5SE) you could screw at least the Bintel one into the telescope side of the diagonal so that when you change eyepieces you do not have to swap the filter between them. You would only have to remove it to view other objects. Not an option for Tim's Newtonian though.