There's a couple of problems with that tank. One is that, as drawn, the wheels will turn in opposite directions. Another is that, for as few people as would fit into it, the weight needed to provide effective armour would be enormous. So, slow speed, and don't use it on soft ground. And it couldn't really cross any sort of obstacles.
I've always wondered what these things offense was supposed to be.
As a p.s., the Hussites used war wagons very effictively, so i'm sure these could be used in some way.
Yes, this was all discussed (and I believe we're all taking the info from) that Da Vinci BBC program (and it discussed how Da Vinci made mistakes on purpose so no one could copy/use them). Apparently, installing small cannon would be very deadly, as the shots would hit the knee and cause a LOT of disruption.
Also (I don't think it was discussed in the program) think of the terrible effect on the enemy's morale. Big thing without horses coming towards you, and it desn't look like there is an assailable spot. It could wasily provide cover against swords and arrows, and it's not like heavy cannon was all that great back then.
Battles being changed? Well... I'm no expert at renaissaince times, but whoever uses it and develops it effectively first will cause all the others to jump on the idea (especially whoever lost to the tanks).
Oh, and one could just shoot arrows/musket out of it, too. I had the idea to do this TL, but decided against it.
Someone putting it to good use might be Poland. IIRC, they could accept the idea, and they weren't inadept at such things.
Also, pushing this forward might lead to otyher advances in technology earlier, particularly those revolving around the tank (aiding it, destroying it).