i have 2 of these, and genuinely: i have to say they are absolutely sub-par in terms of functionality.
audio is pretty good, especially in stereo. but this is...when it works.
something that isnt made super clear, to start: your homepod minis must be on a network together in order to use their stereo function. you cannot somehow do this over bluetooth, or the UWB they can communicate over. remove from wifi and suddenly you can only use one at a time, in spite of the ability to say, share audio between two different sets of headphones. this is an obnoxious limitation considering the homepod minis COULD be portable if paired with a good USB-C battery pack.
the rest of the time...by god they are annoying to maintain connected. i have them setup in the kitchen, and most of the time try to use them with the latest ipad air. sometimes when trying to stereo pair, both will connect but only one will play audio. sometimes they'll play both as monaural so you get this odd echo. often the audio will just drop entirely yet they'll still be "connected".
these issues plagues us with the latest iphone 12 pro max, as well as the aforementioned latest ipad air. my home network is robust, and quarterbacking it is a powerful wifi-6e enabled router. (yes, i am aware these devices will not take advantage of the 6ghz band or 6e protocol, this was a point of reference to note that my network hardware is not old or cheap.)
i have tried unplugging/replugging. disconnecting/reconnecting from wifi. factory reset, etc. turn off/on the ipad/iphone. all of these devices are running their latest software updates.
probably the absolute most irritating aspect of this is how long it can take at time for the devices to switch between audio outputs. especially when the homepods stop playing audio, i've become disinterested in spending any further troubleshooting time so i'll try to switch to the device's speakers. only to be met with the spinning wheel for upwards of 10s at times. for the apple magic, this is absurd. why does it take any additional time to switch back to onboard audio? windows PCs do not suffer from this problem. if you want to swap audio devices, indicate this and bam, Win 10 accomplishes this *immediately.*
i hope others with the product do not suffer from this problem, but i cannot recommend these at all, even on sale.