Intercom is not all I thought it would be. I would certainly not make it the basis for buying the HomePods.
Basically, imagine that you record a message, have Siri play it on another HomePod, the person on the other end records their message, it’s playing on your HomePod, each step accompanied with Siri interaction. It’s just too slow and somewhat convoluted.
What they should have done is to create an “intercom mode” where everything said on one end is automatically played on the other end until one side exits the mode, without the need to separately initiate every reply via “Hey Siri”.
Also, I believe IKEA used to sell a Sonos made Homekit compatible smart speaker for around $70. May be a worthwhile alternative to at least consider.