If you want to see data from all three Blynk accounts in one mobile or web dashboard without having to keep logging in and out then you’d need to use either the HTTP(S) API or Node-Red to send data from one device to another via its Auth token. The fact that these devices belong to different accounts doesn’t matter - Blynk doesn’t do any checking of this.
To make any changes to the datastreams or dashboard layouts, or to send firmware updates via Blynk.Air, then you’d need to be logged-in to the correct account.
One issue that you will have is the default permissions attached to each role in the Free/Plus accounts, as described here:
As far as I’m aware this hasn’t yet been fixed by Blynk (at least the Free account that I registered still has the same permissions as it did originally).
That’s true, but the Pro plan has the ability to change the user permissions for each role, and to create sub-organisations which ringfence groups of users and devices so they are isolated from each other. That makes life much simpler, and (in my opinion) makes the Pro plan a much more viable option for anyone wanting to do this type of thing on a semi-commercial basis. The Pro plan has other functionality too, including fewer restrictions on the number of widgets and greater data retention times, but they may not be a ‘selling point’ in your situation.
The Plus plan does actually have the ability to add an additional 10 devices to the account, but the pricing of this is a bit strange.
The Plus 10 subscription costs $6.99 per month when billed monthly, and the Plus 20 plan costs $12.99, making the Plus 20 plan $0.99 cheaper than two Plus 10 accounts.
However, when you switch to annual billing, the Plus 10 account drops to $4.99 per month and the Plus 20 account drops to £11.00 per month, making the Plus 20 account $1.02 more expensive per month than two Plus 10 accounts.
@Dmitriy - Maybe you should look at the cost of the Plus 20 account with annual billing to make it more like $9.00 per month to overcome the pricing anomaly described above?
Pete.