Which type of Barlow

[ScottS]

I'm in the market for a Barlow (ideally a 2x given the range of eyepieces I have at the moment), but I will also need it to be suitable as a laser collimation aid for my 200p Dob. I can obviously do the shopping around myself, but I just need to know if there are any type of Barlow's (long, short, 3x, 5x etc) that will not be suitable for both applications in this scope. My laser wanders around all over the place in the focuser on it's own So, anything I should be avoiding? Thanks. Scott.

[ScottS]

Thought I read somewhere that the short versions were unsuitable for Barlowed laser collimation? Is this true?