I bought 2 HomePod's, however competition is extremely tough in my house.
In my bedroom I have Dali Zensor 3's coupled with a BK Monolith Subwoofer.
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Downstairs I have Dali Zensor 7's, with Dali Zensor 3's as surround and a Dali E12-F Subwoofer.
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Now comparing the HomePod to these 2 setups is not fair at all, but my standard are set fairly high. However, after spending time with the HomePod, letting music play throughout the house for a few hours between 20-50% volume (not touching or moving them), the sound seemed to get better (I know speakers can need a little run in period). I started by just using once, getting use to it, how it works, things Siri could do. I thought the vocals and clarity was very good, with bass being very nicely balanced and not overpowering (of course you need a good source, I was playing .AIFF files from iTunes).
It changed when I put the other one on. Wow. These 2 little speakers playing together, roughly 8ft apart, sounded incredible, albeit not true stereo (yet!). Siri worked perfect for me still, only resulting in 1 speaker dimming the sound, it had no trouble hearing my voice. In short, if you like your audio, I would try and get 2 instead of 1 as I don't think someone who likes their audio a fair bit will be too impressed. The ease of use, ability to move it to another room is very handy. I will probably end up buying more in future.
Siri is nothing special either, its just like an iPhone or iPad, yes its not great compared to others, it gets things wrong often, it's worked ok for me so far, but this is all Apple's side that can be improved and updated.