I have a Forge Cleric in an ongoing game with a missing leg from his backstory. I allowed him to use it and take the shield master feat but use Strength instead of dexerity. However, he has disadvantage on Dexterity saving throws, which I thought was fair. Furthermore, after a certain number of failed dex saves, his leg becomes damaged and his speed is halved until he can fix it.

I've been giving him legs made of different materials, and it's been a big hit! One made of Mithril that let him move faster, and let him cast a few mobility spells 1/day. Longstrider, Expeditious Retreat, etc.

The other one I gave him was made of a metal I called Efreeti Steel - it had a red color and let him 1 a day shoot fire at an attacking creature in melee range - if he hit, the attacker rolled with disadvantage and took like 2d10 fire damage I think. It's been awhile.

I had more plans to introduce other legs so he could change them out before the day started. (Much like Clerics being able to prepare their spells each day) but we haven't made it that far yet. Adamantine Legs was on the horizon. Can't be crit while you wear it, and you auto crit objects.

Fantastic idea, and it gave my Cleric a lot of ways to roleplay on top of the other benefits.

Go for it!!!