Although this is a "small" and when I say small i mean very "small" step towards basic security.
This mod should in no way shape or form have someone beleive their site is secure by installing this.
Although this stops a portion of sql injections it won't stop 100% Xss attacks, LFI or RFI at all, -999999999 type injects, session Hi-jacks, or csrf attacks.
So while it stops some, it misses others completely. Where as securing your site properly by making sure all GET AND POST variables are sewed up properly will, this script won't.
A con is that occasionally this mod Will bug. Randomly upon visiting certain pages players will get Malicious Request detected for no reason at all.
If you haveno security i'd recommend this, but i suggest securing your site properly over all.