|Keep laughing...the foot lock seems less humorous after you can't walk.|
I'm not a big time seeker of leg locks in rolling, but when they present themselves or when nothing else I'm doing from the bottom is working, I'll sweep from the kneebar position. If I'm having trouble passing the guard, or the guy has defended the ankle lock well, I'll switch to the Comprido, or figure four toe hold as it's also called.
At any rate, weeks ago, in the gym, we were lined up, then paired off, and the rules were to roll until someone gets tapped. After at least 20 min's with another blue belt, we were at a standstill. From bottom, b/c of my knee, my go to triangle wasn't an option, and from bottom his armbar defense was better than my armbar offense.
He was shorter, stockier, and a good bit heavier and close in technique. I'd get to half-guard, sometimes to sidemount, then mount, but with my knee injury, I couldn't maintain mount and hunt for a collar choke the way I normall would.
I'd get swept or stuck in half-guard then swept b/c I had to careful with my injury and couldn't fight the half-guard position by basing out.
After about 20 min's, I hit a Comprido/figure four toe hold. Then I did the same to the next 2 guys I rolled with.
That being said, Judo has leg locks, depending on who your instructor is and what rules they abide by in the gym.
Back in the day, one of my Judo coaches taught me a turnover or two from what I now know to be a straight ankle lock. It's a bit different from Mifune's turnover to what is basically a boston crab, but it is similar:
Richmond BJJ has a brief article about the efficacy of leg locks in BJJ as well.
That being said, passing guard to side mount then mount or back taking should be your priority.
However, you may face a player who's guard retention is better than your guard passing.
You may be down on points. Or, perhaps, he leaves his foot exposed right near the start of a match....Capitalize! Finish the match and continue on to the next portion of the bracket.
If you finish someone with a legal submission be it choke, armbar or foot lock, it is part of that division and legal. The recent ADCC was proof that especially in NoGi, leg locks are an absolute necessity the way wrestling is.
If the mantra of Brazilian Jiu-Jitsu is "what works".....then a personal or inherited prejudice to foot locks is only overlooking and ignoring a set of submissions that work, even at the highest levels of the sport.
As with most things in Brazilian Jiu-Jitsu and submissions.....respect them you must....or disrespect them at your own peril.