Making your own beam expander is great, I have done it with the M-140 by putting lenses in cardstock tubes so that I can slide it to focus.
But if your going to buy one to work with most all our MM diodes try a sanwu 3X, if nothing else you can compare to the ones you build and I may well use the 3X input with a larger output lens further out of course.
Or you can do what i did and ask Mr ElectricPlasma to 3D print lens housings that accurately and squarely slide together and house to input lens vs the output lens and printed to your specifications such as the beam expander i'm using right now !
This is the very crude original design drawing i gave ElectricPlasma and he took that and drew it up in CAD and printed it !
Just an update for anyone interested, I've got the alignment of the lenses the best it's ever been, I figured out there was some twist of one of the cyl lenses vs the other and with that fixed my homemade beam expander could squeeze the dot at 55 feet to the smallest it's ever been 11mm x 5mm and at 15 feet and with the newer NUBM44-81 8+ Watt diode it's insane now !