I had researched shin/knee guards early this year, looking for specific features...I wanted something that had good coverage over the knee (above the knee and both sides).
I wanted something that bent with the knee but also have a shin part that wasn't too long. (that would interfere with boot). And if possible, fit under regular jeans.
I considered the MX guards, but they were too big to fit under regular jeans... and the smaller knee guards, like the KNOX Cross Knee Guards seemed like they only covered the front of the knee.
This pair from Thor seemed to have all those features I was looking for, and I was able to find them at GP bikes for about $30.
http://www.webbikeworld.com/r4/thor-knee-guards/
The coverage is good when first strapped in, but they slide down when riding. This could be because the top straps wrap around the calf, and so will naturally slide down with movement.
If I were to strap them higher (right behind the knee) then the knee part of the guard would sit too high, and the top part of the guard would stick out when the knee is bent (yeah I know, kind of hard to describe)
The guard is 2 pieces, and looks like it would articulate with your knee, but it doesn't...the 'joint' is positioned below the knee, so it doesn't bend with my knee.
(unless I'm wearing them incorrectly)
BTW, I am able to fit them under regular jeans(tight at first, but the jeans stretched a bit)
Also,I'm thinking of adding a third strap to the top articulated part of the guard, so that maybe it'll hold in place better.
Overall, they're alright ...and for $30, if they're not to you're liking...you can always get something else, without feeling like you wasted a lot.