Noted 
now let it restâŚ
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As @zodiac has said, they have 1MB of memory, so work fine with OTA.
The issue is that some FTDI interfaces canât provide enough current to power the Sonoff properly if you want to test the new functionality while itâs connected to your PC.
Youâll usually get it to connect to Wi-Fi while youâre powering it from the PC, but the relay(s) may not energise correctly. This can be an issue if youâre tweaking your own code and youâre listening for the relay to click-in and it doesnât.
The âproperâ solution is to beef-up the power that youâre feeding to the Sonoff by using a separate 3.3v supply (with shared ground connections). This allows you to do all of your bench testing and see any serial debug messages on the PC. Of course not everyone has a separate 3.3v supply, which is where the temptation to plug it into the mains while itâs still connected to the FTDI programmer comes from.
Personally, my life and the well being of my PC are more important to me than spending a few [insert local currency here] on a 3.3v power supply.
Even if I was using North American 110v mains I donât think Iâd try it.
The only flaw in @marvin7 argument is that should one of the components in the Sonoff circuit fail, it could result in mains voltage finding its way into the FTDI programmer. With modern earth leakage trips, its likely that even if you did something really bad, the trip would save your life, but the same might not be true for your beloved PC.
Have fun with the Sonoffs, theyâre amazing value for money and surprisingly well built and reliable.
As well as using the S20s for controlling plug-in lights etc around the house, I have a couple wired into my outside lighting. The lighting normally operates on a PIR sensor, but there are times when I want to override this for longer periods of time. We have a back âyardâ (as you would probably call it) that we use for BBQs. Once the beers start flowing and it starts getting dark we arenât always ready to move indoors, and itâs annoying when the PIR detectors pick-up a bit of movement and switch the lights on for a minute or so then off again. I have have a Blynk switch that allows me to switch the lights on for a preset time (usually 1 hour) on a timer. This activates the Sonoff Basic thatâs wired into the lights to keep them on regardless of what the PIR is doing.
I have a similar setup at the front of the house where if its dark the lights come on automatically for 5 minutes when we open the gate, and this gives time to park the car and unload it without having the outside lights switch off too soon. I could obviously adjust the PIR duration, but that would mean that were on for too long most of the time. Itâs also handy if Iâm working on the car and it starts to get dark, I can use the Blynk timer to put the lights on for as long as I want without the annoyance of them going off at an inconvenient point.
Okay, drifting off topic a bit here.
My rule is donât mix mains power and PC logic signals at the same time. If you do then be sure you know what youâre doing, and have a change of underwear handy for when you do something stupid.
Pete.
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Sorry, I was busy typing when you posted that.
Consider the topic dead and buried.
Pete.
Thanks @PeteKnight, that was nicely informative. PS, I donât care much who is right or wrong⌠all opinions are valid in their own way, but constantly battling it out is a bit beyond this forums purpose as it is not a Blynk relevant issue
I really look forward to learning how the Sonoff works with Blynk⌠I will be sure to beg for some code 
Uff⌠what a pleasant reading 
I deleted a long post just before posting after reading thisâŚ
And⌠Sonoffâs are great, and I couldnât live without them already!
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Thereâs already a code I have posted in regulars lounge, it does everything you need, so no need to beg for anything.
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Thanks Pete, well worth repeating.