These writs are for only 2 vouchers, and require 20 max level, triple-reagent poisons. I get a lot of these, and most of my friends do too.
First up, the quantity is wrong, because it leaves you with useless poisons you can either save for months until that same writ comes along again, or vendor them for almost nothing.
Next, for 2 vouchers these aren't worth completing. The materials and time involved aren't worth the 2 vouchers. For 3 vouchers, I'd probably feel like this was a fair time/material exchange.
Finally, the number of poisons should be changed to be a multiple of 16, since the writs ask for poisons that will have no trade value outside of these writs.
I would recommend changing the number of poisons to 16 if the writs will remain only 2 vouchers, or 32 if the number of vouchers is increased to 3-4. If they increase to 5 vouchers like the writs requiring a max level, triple-reagent essence, then 90 would be acceptable (meaning it would require 5 'crafts' to complete like the essence writs).