yes, the chemical is sethoxydim. Poast, arrest I think are the same ...about 150 a gallon but it dont take much.
Sethoxydim is a grassy weed herbicide. Henbit is a broadleaf. I dont think it will help you.
Slay is Imazethapyre and will work. Use the mid rate as the high rate my hurt your clover. I would use a surfactant also. Do a follow up spot treatment in 2 or 3 weeks.
John
A less expensive alternative to Slay for general broadleaf control in clover is 2,4-DB, sold as Butyrac 200. WARNING: 2,4-DB is not the same as 2,4-D. DO NOT use 2,4-D on your clover as it will kill it. Unfortunately 2,4-DB (Butyrac 200) is not effective on henbit.