So, I am going to say 1st off congrats on getting to this step and publishing this.
I apologize if I word something badly or what not just ask me to clarify. Also I will say upfront that some of this is just personal prefernce as well.
I think the content over all is good for someone who doesn't already have another shield system in place. I like the Shove and Stun mechanic except I think it should be a choice to deal damage or do the shove / stun. . I think if you look into Kolbold Presses Beyond the Damage book what you have reminds me of how they do some weapons with special features. I love the idea of the additional factors with the Feat.
There are a few things that I think are not going to work well with some of the things you have listed.
Large shields 3/4 cover option seem weak to need such a higher requirement to use it. 3/4 cover is easy to negate by the enemy shifting aound the enemy without leaving his threat range. If you assume the character pivots that means their back is no longer with 3/4 cover which means his back is exposed and other enemies can attack him without his cover mattering. I think the Tower shield idea is great, but i would add a strict 3 armor to it and still have the cover concept with it.
I find it strange that the small shield does more damage then medium shield Also there is no prices or wieght.
I would think finesse would be good to include on the light shield as it is something I could see a more dexterious player picking up.
I would add Heavy Shield Profiency to some of the classes as the Tower Shield takes generally a lot more training to use properly on a battle field. This also is good for someone like me who runs the Ecumbrance variant where strength isn't required on armor.
I think there is a lot of wasted space. This could be a me problem though. I am on a 2g (less then dial up) internect connection so the file size took awhile to download. But over that I think that the space was just stuffed in. Page 1 is cool. Page 2 I feel could be moved to the website DMGuild page. Same with the credits at the end.
I feel that there is no need for a table of contents. There isn't enough here to warrant one plus I assume all PDF readers have a content feature built into it, but maybe not idk. I honestly think a clean table with all 3 shields would be better then all the space that is taken up. There also was some wierd thing where each page had a 2 inch (guess) white bar for some reason.
I don't think there is anything wrong with the content at all and I think that overall it would work just fine as it is, but I could see some approvments. I didn't even get into ideas I have about bucklers vs light shields ect ect. That is not for me to just throw in here. Thank you for taking the time to make this.