Yea, was looking into it and don't think it'd be a good idea to use now, 5th week into flower and they don't need nitrogen no more ( well as much if any ). Just going to keep them for next grow and continue using Root Farm.
Yes this is years old, but someone might stumble across it.
This is my experience with Jobes Plant Spikes
I've used the Jobes Plant Food Spikes 13-4-5 about a quarter way into veg, also used egg shells for calcium and coffee grounds for nitrogen.( Just got to because careful because it is...