Mmmmmmm
They say that they are members of ATOL on their website but I have been trying to find any reference to them on the ATOL website and there is nothing coming up for a member company by that name.
The don't supply an ATOL number either.
They say in their about us page that they are agents for ATOL protected tour operators, this would only give you some protection if the actual operator went bust not if Sunmaster got in to financial problems.
Unless somebody else is able to give you more specific details about them i.e. booked with them or has dealt with them I would be inclined to avoid them until you get more information.
Sorry I can't help more than that.
Graham