Something wrong with voting on this thread wanted to upvote Angus's post but the vote button is greyed out. Have only just opened this post and not voted on it?
I recall one of the devs saying that they were quite surprised that we could open multiple clients successfully, they were not unhappy with the results.
as jflat says he and others are working with a legacy system written by scientists
I am continually amazed by the uptime and functionality of foldit
Back to the point - when you open a new client there is an opportunity to skip the download which starts automatically but you have to be quick.
It may be preferable if possible to make that event a user selected/agreed download rather than an automatic one, so when you as a user open a new client and a new version of foldit is available the process will start but nothing will be downloaded to your personal device until you have explicitly approved the download.
This would be in line with expected download processes in 2015
At this point a warning message could also be included recommending that you close all other clients to avoid unpredictable consequences
Personally when I open a new client I know I have to watch the first screen carefully and be poised to hit the skip button.
I never accept a new download without first preparing - and do keep separate copies (backups) of the all macro file so I can access favourite scripts quickly to catch up.
Some players like to keep old versions of the client, which may be good practice for gamers, may not be much use if you can't play new puzzles
so to avoid issues, close all clients before accepting an update and watch the screen when you open a new client so you can stop the download.
BP and others can provide better advice on impacts of a new client download on one device across multiple concurrent endpoints.
If you run devprev you are implicitly accepting the risk of unpredictable behaviour in the new client and possibly different scoring results as well.
The point of devprev is to test before sending the release to main it may affect your score for a particular puzzle, your choice to play using devprev rather than main.