elhigh
Why sell M at all? L-pipe is nearly 50% thicker wall in 1/2" pipe, it's tougher and easier to live with.
If L is cheaper, leave the M exactly where you found it.
P
At least on their website that's not necessarily the case. Make sure you are comparing the same diameter pipe. Otherwise my guess would be they don't sell much M type pipe since it's not supposed to be used for plumbing applications so it ends up being more of a low volume specialty item.