I use Netspark for Android, which is on the one hand excellent for the purposes it is built for, but on the other hand can get slightly buggy at times. It works with a VPN, which is a huge advantage, I think, over others…and I use the Chabad beis din as admins so it keeps the device fairly choked up to the minimum (with the extended plan still offering plenty to work with). I found a loophole that works on my phone, and they fixed it for a while but recently they removed the fix, which is annoying but I won’t make a fuss about it again…
I was seriously considering getting the version of Gentech for Android phones which basically erases all of your apps except for a few pre-selected ones that are essential, but they don’t include essential apps for Israel, and therefore I can’t do with it.
On my PC I have Gentech, which is excellent and had several advantages, with one weakness (in my opinion) being that it doesn’t use VPN like Netspark does (which means that it is open to loopholes…). But it does the job wonderfully, all in all.
I used K9 for a while, but found that it is ridiculously easy to bypass. I have heard in the passed of a very expensive, yet absolutely top-of-the-line filter, which works better than even Rimon (which isn’t enough to stop the absolute tech-savy obsessive from bypassing). There was this site which went through every single possible loophole for a filter, and why they, as professionals, were able to develop a filter which is indestructible.
Anyways, because of its price I quickly forgot about it…