Wow, thanks for the review! We're so glad you liked it!
About the optical sensor: that's a great idea, we think about that from time to time. We have some ideas about doing several different versions of uECGs for different purposes, still not sure if we'll do that, but we'll certainly consider the optical sensor, because (like you said) this would give lots of new data.

About programming nRF52832: do you mean the tools? We use STLink with openocd on Linux.

On working with PCBWay: that's actually pretty easy, because they have a lot of the process automated - like choosing the parameters of PCB/PCBA (assembly), uploading gerbers and BOM. After that, they answer you with a quote and some questions if they have them, and then you pay for the order. That's for PCBA, PCB orders are done without discussion normally.
The real work if you're looking for PCBA is preparing the BOM, like making a really detailed one, filling all the P/Ns and descriptions and making sure they can buy these P/Ns easily (you can check on LCSC, even better to fill LCSC product links in BOM). And communication is important too, keeping it short and using direct, simple English helps a lot. You can also provide them with stuff like pictures of LED polarity (we like to do that every time, especially for RGBs). Best to start with PCB without PCBA if you're new to this. But if you have low component count in BOM, maybe you can try PCBA at once. Good luck!

P.S. Sorry for slow answer, we're taking a small break in January

Hi, Guiseppe! Thanks for supporting uECG and buying two versions of it!
We have written to you after the review but unfortunately haven't received an answer :(
Anyway, we'll answer here too so maybe you'll see it.

First, we're glad that you liked the device! We are working on it all the time.

Second, about the shipping: initially you caught some really slow moments when ordering the device - during the height of the pandemic and even now, the shipping to Italy is very slow. We're sorry about that! We're tracking all of our shipments and write to support when we see it stuck, but there's not much we can do for the shipments to move faster.

Third: communication is actually usually very fast on our end! We answer on the same or next day, depending on the issue. Although we understand that you may feel that it's hard to convey to us what you need because there's no clear process to do that, you basically have to write to us by email or on Tindie/Hackaday/YouTube/FB/Instagram at this point. We're thinking how to make feedback faster, maybe we'll make a forum or subreddit.

And last but not least! rMSSD is now implemented and is already in the newest app version on Google Play (https://play.google.com/store/apps/details?id=com.ultimaterobotics.uecgmonitor4_2). We have actually been working on it when you wrote, because another user requested it. It's actually the fastest way to get us to add something - when users say they need a feature, we add it to backlog or implement soon. Also, we added saving to PDF in the app! ECG is now plotted as multi-page PDF file with 1 page per minute, each page has a timestamp, average BPM and 5-min average RMSSD. If "mark" button was pressed during that minute, also adds purple corner in PDF with mark ID. Now app saves both .csv and .pdf files after recording.

Anyway, thanks for the feedback! We'll try to make it easier to request features and communicate with us in the nearest future!

Kseniia,
and the rest of Ultimate Robotics team