For my personal preferance, when I'm ordering something thru VRS, or sometimes some bill payments, I rather for VRS interpreter not to explain and just talk as it is. Other time, if its to a regular hearing person who have not experienced VRS, might get hung up once in a while, but I'm more patient to allow VRS to explain their role to regular caller, not when I'm ordering. I do not like being hung up more than once, which results in for me to go in person to the place I attempted to order from. I don't like conflicts, just trying to go as smoothly as possible. Or sometimes, like in middle of ordering, explain the role as VRS and they cannot hang up once they realize they have customer on the phone! $$$!
It depends on the person's preference on whether to announce VRS call or not. Mostly, its related to ordering, so don't worry too much about it!
Keep up your best and interpret for the caller!