Having read concern raised by
SubMash when using with low sensitivity IEM's I still decided to give it a go after having tried an ES100 at about £89 but not being happy with controls/materials or design (but did sound great with my SE846's & HD660S over LDAC).
The BTR3 came today for ~ £49.50 (£55 on Amazon) and basically the build quality is everything the ES100 isn't, super easy to operate with phone or as a DAC to PC, and initial impression is it sounds as good as the ES100 via 3.5mm jack. Only tried with my SE846's but will try with my HD660S tonight. No background noise I can detect with the SE846's either. The V30+ wired using QUAD DAC does still sound a bit better but can't say there is a lot in it when listening to Spotify or Tidal MQA tracks. Looks like it will be great as an alternative to using my V30 wired or better than most other phones audio.
Nice upgrade to my old HS3000 AptX BT adapter (which still actually works with around 4hrs of battery after around 5 or 6 years.
Unless you need balanced, app tweaking and longer battery life I'd go for the ~£55 BTR3 over the ~£90 ES100, especially if design/materials/looks are important to you. Oh, or need to drive more demanding headphones.
I tried the other lower BT modes including SBC, AAC, aptX but AptxHD and especially LDAC set to Optimised 990kbps sound noticeably better.