Yeah, that was me with the shield at the Cajun house. In fact, another friend of mine had one too, and we did one stack of four behind each shield. I think in that particular objective we were outnumbered and hunting the rest of the building (fairly large with a 'street' and some side rooms). It was made of plexiglass painted black, curved using 3/4 ply cut on a bandsaw, with a clear plexi window about 2"x4" near the top. The thing was only about 3' tall. I had it on point with Kurn's Glock 19 and was able to sight through the view port, which actually worked really well. The center (about a 14" x 5" area) was thin cardboard, but since it was dark, it took awhile for anyone to figure that out, and all the shots came in more towards my head and bounced off harmlessly. So, not only was I crouched completely behind it, I was putting out fire with the pistol as Ninja covered me over my head, so it wasn't like I just turtled my way out with impunity. We moved quickly and fired fast. It was actually quite funny coming up on members of the opposing team and letting them see it for the first time. The biggest response was "Oh sh*t!", followed by diving for cover. Once the newness wore off though, it wasn't nearly as effective, but if you know how to use it, it was a formidable piece.
IMO, bottom line with a SWAT shield is that you can't make it invincible (hence a carboard center), you can't make it a fort on wheels by making it too big, and you have to incorporate some kind of drawback into its use (ie, make it heavy with some weights and restrict any weapons use to a pistol only). Mine broke recently and I wouldn't build another one unless we had some dedicated CQB action that was pretty guaranteed. Also, I built mine specifically for use at the Cajun House, so as long as you have realistic expecatations about when and how it can be used, build away and have fun with it!
