One way cubes sounds like a better options then theses ;p you can do so much more with it.
also all these methods fail to stop grenades from going through (or the spiders weapon - or gibs or debris; which may make this look a lil weird.)
(Basically for all the coders out there anything identified as a bouncer and uses physics not just point detection, It would be nice to have a game-Noclip that didnt allow people but bullets, and a player-noclip that allowed players but not bullets, but for now we have to hack it).
The correct way is an odd shaped cube (called a one-way cube). There are many versions; the one you need is on the map europium. (Its easier then trying to explain how to make it). It is located inside the base doors (brown wood) (its a cube of the smallest grid size textured skytexture just copy that one and paste it into your map, You will need to lay a grid of those across the space you want to be "force field" then you can apply any alpha or what ever, just make sure you set skytexture 0 so you dont see the one-way cube.
PS: These cubes can be a lil buggy sometimes so be careful how you use them! Make sure you do plenty of testing.
PSS: You can not jump while inside these cubes so making them more than 1 deep may cause a problem (so x by y by 1)
PSSS: Using the smallest size grid is ideal you can use larger ones, these faces can be pushed to be even smaller (if wanted) (uses f+scroll - q+scroll may lead to problems)
PSSSS: Alpha is better than glass in my opinion, more options, and the ability to overlay, crack the glass etc.
PSSSSS: Idk what P.S. etiquette is so dont kill me for all the "S"es :)