Home expansion tank - water hammers

Hi -

I don't know if it is code or not but we have a 5 gallon expansion tank
plumbed into our hot water line upstream of the HWT.  I think it's purpose
is to prevent the pressure relief valve on the water heater from operating
too frequently.   As a side benefit I assumed it also absorbed water hammers
but I am wrong.

I would prefer to remove it completely from my system and instead install a
water hammer supressor.  Not sure if those actually work (any feedback would
be apprec.)  The expansion tank just has to be a code item.  Any suggestions
on where I should look for this code?  I think the tank is useless and want
to save $50 if I can.  Any help apprec.