Xavan pond liner/ pond lights

I am considering using the tetrapond Xavan liner instead of a Butyl liner.
The main reason for this is the weight issue, overall I going to need about
9m x 8m of liner.

Has anyone had experience of Xavan, in particular they claim that given its
strength it doesn't need an underlay, this helps keep the price in balance.

I am also looking for some under water pond lights that have an outside
transformer and can connect into the same block as the pump etc. The only
ones I have found arethe OASE. These appear expensive, are these worth the
extra as compared to other makes.

thanks

David