Certainly not a bad shield, assuming it blocks 50% damage. The upgraded version is cheap yes. I can't figure if the upped shields at 4 quanta ought to block 50%.
- Turtle shield is similar effect at 4.
- Improved fog costs almost nothing and blocks 40%.
- Permafrost has a good chance of blocking at or OVER 50% with added freezing. I didn't count it though. Cost is much higher at 7.
- Fire buckler does damage at 4, so it's a different effect. It won't block 50% but it's help killing.
- Carapace blocks 1 and does damage at 7. Different effect, on par with buckler. Poison stacks so it should damage a bit more.
- Jade shield blocks 2, but has 2 abilities. Good at 7.
- Titanium is going to cost 4 and diamond 6. So, does the diamond shield block over 50%? It does, if the avarage attack is under 6. When is that? Not often if you ask me. It is a good lock on skeleton and ffq decks, so that should count for something.
So I'll say turtle shield/fog/improved dusk are fairly cheap for what they do. If any change is needed, the lot of them need a cost increase of 1.