Just my two sense.
The DSE-905 IS a copy and a bad one at that. I bought one right when they came out just because they were cheap and I wanted to see what the difference was. The 905 has a plastic connector between the bat case and the atty so that the led can lite it up, bad idea!!! This connection can break the first time you drop it. The original SD is made much better with the exception of the rear mounted switch that can break off if you drop it and it lands just right. There is a reason thy they sell replacement switches for the original. I have two original SD's that work great but I have done some tweeking on the switch to prevent it from breaking. The average user should not have to worry about such issues but it is a very well build unit.
I have recently purchased a new devise from a site called powervape out of the U.S. that is made very well and has the switch on the side. I've only had it about two weeks and I don't use my SD's anymore because I love the switch placement on the powervape.
The powervape is almost identical to the SD in construction but the switch placement makes it more user friendly. Powervape is located in the U.S. so the shipping time was like three days and it was cheaper than the original.
If you are looking for one or the other, definitely get the original SD before the DSE-905.
If you want to save some money, check out the powervape.
Good Luck!