3rd update Mar 20, 2019:Updating my previous, original 2-star rating to 5 stars thanks to their support given and a fully functional replacement device in ~2 weeks.--- TL;DR ---My initial experience from Sep 2018 with my DUO was mixed. I didn't contacted support, and wrote my first “quick review” on Dec 2018 or Jan 2019. On Feb 2019 I got contacted by a person from support because my review.Since then, the support person 'greatly explained' the causes of the issue and guided through the process for getting a warranty device.I'm very placed with the detailed support given by him, and new replacement device works great!--- Device ---My issue from Sep 2018 while RX mode was indeed a defect on some units on the Amazon warehouse from that period, which occurred in any codec (SBC, aptX and aptX LL).The TX “issue” of audio fading/cutting on low volume (e.g. while playing on Nintendo Switch on low noise scenes), is normal. One must turn all the volume up on the audio source so the device can capture it, as the chip isn’t an amplifier but just a transmitter.Due the RX issue, I was offered replacement device. Decided to try and upgrade to the Trond DUO S. Now I can confirm the intended correct functionality of RX/TX on both devices (DUO and DUO S), and confirmed the RX firmware defect.Additionally, I could test pairing a DUO with a DUO S. They work amazing on aptX LL (Low Latency) which is selected automatically as it’s the best codec available on both. You can easily see and hear the difference between the standard SBC and aptX LL, the latter feeling instantaneous on audio visual feedbacks.After 5 months of use and having a fully functional unit...Re-viewed PROS:- Compact goodness.- Good battery duration, easy charging, and can be left connected.- Easy pairing, even multiple pairing (after you get the “trick” for pairing).- Lot of adapters included.- Long satisfaction warranty (18 months) and great support service.Re-viewed CONS:- No configurable low-battery audio signal. It can confuse you from phone alerts, etc.- No configurable LED.--- Support and warranty ---They are serious on their support area, as they followed me up some time latter from my original 2 stars Amazon review on all my emails until I got the issue solved (on my case a warranty applied, until I had it on my hands, even though it would need a global shipment).They DO respect their “18-MONTH TROND warranty” additionally from the Amazon return period, so you can buy with confidence that any defect will be followed quickly and in great detail. This was getting replied the next day and getting detailed explanations of the cause(s) of my issue along with the possible actions to take.Big thumbs up for Trond. They managed to stand up with the pesky support processes of many other bigger companies out there.--- MISC ---My only complaint could be their webpage. Before making my original purchase, I looked up their website and it feels empty and outdated, like if they didn’t exist nor could give any kind of quality support in case you got into issues. They deserve a newer and better site that shows and highlights their great client support.-------------------------------2nd update Feb 22, 2019:Their customer service contacted me regarding the issues I mentioned here, trying to help me with them by proposing a replacement thanks the 18-month warranty.I will try keep updating this review accordingly.------------------------1st Original review:Has been some time that I got this (Sep. 2018) and have been postponing a quick review, some thoughts on this device.I have used a few times on various scenarios (playing on Nintendo Switch, video watching, etc., with different headphones as receivers, and different controlled sources as high end phones and laptops).Personal cons:- 1 issue as a receiver.The device is identified as apt-X on my phones, but the output audio is awful, sounds muffled, as phone call quality on all devices that I tried.This reaches the point that the Windows 10 "bells sound" sound test gets very pitchy and gets highly distorted and the very end of the last bells. I would like to provide an example of this by recording the output from the Trond when used as receiver.- 1 issue when transmitting.When transmitting, the quality is pretty good, BUT, when having low volume sounds coming from the audio source, the Trond seems to "fade" or cut-out the audio.Playing games on the Nintendo Switch is not enjoyable with some games that have some low-volume scenes, since those are intermittently faded or cutted-out. There is no noticeable delay at least from what I can tell (but at this point I just stopped using the Trond both as receiver and transmitter).(As I said, the quality is great when transmitting, but not sure if it's real aptX quality grade, my headphones don't have any indicators of what protocol is being used when receiving audio from the Trond when it's transmitting, neither Windows helps with this).Pros:- Super compact, portable.- Portable power of ~6 hrs or more.- Quicker setup as receiver.- Can be used always connectedNote that I probably got a defective device but.... Anyways, I stopped using it since then (Sep. 2018). It has just a couple of days of usage. Recently I got the time use it again but as a background music receiver, as the previously mentioned issues are just annoying.The receiver sound quality is the dealbreaker for me.Maybe is normal for the price, just the aptX is there for the short delay feature of the protocol.