For the price why wouldn't you get the MX?
Supports up to 30", not 24" and supports up to 30lbs, not 20.
I have the MX and its slick as f***! Looks futuristic compared to the LX.
why not just get something like this from monoprice for 1/5 the price?
dual monitor: http://www.monoprice.com/Product?c_id=109&cp_id=10828&cs_id=1082808&p_id=5560&seq=1&format=2
I've had 4 of the monoprice ones. They WILL SAG. They are NOT stable ( forlarge monitors, at least).
They barely held up a 2209wa. I've tried both the non-articulating as well as the 3-point arms and I was NOT happy with it. I love monoprice but if you are looking for a reliable mounting solution, you get what you pay for.
What do you mean by lock?