Thanks. I just got an email including your note 
In answer (I think) to your question in the note, the only way to make a one-off payment is via the Paypal link on How can I donate? , otherwise (as mentioned on that page) a monthly or annual Kee Vault subscription would require the full sign-up to Kee Vault (supplying an email address, master password and then a credit card before the free trial expires).
The redesign is initially focussed on the popup, with the idea that once I’ve got that overhauled I’ll be able to delete the “save” dialog with that old clunky UI and replace it with something inside the popup (and that won’t always have to be invoked in response to a form submission event, potentially helping with that workflow of registering for a new account). So far I’m pretty happy with the appearance of the popup but I’ve paused work on it until I can be sure that it’s a feasible architecture for a WebExtension (and with an eye on all the Chrome extension features Google will disable in the coming months).
I’m using the branch on my own machines BUT avoiding the search feature since this seems liable to crash the system intermittently (at least on Linux which doesn’t handle memory exhaustion as well as Windows). Until I can work out why a simple text search causes rapid memory growth, I can’t commit fully to the ideas I’ve been exploring in that branch so please either take that advice on board or, if you’re a Vue.js/WebExtensions wizard and can follow along the code in its unfinished state, point out which stupid mistake I’ve made! 
I’m reasonably certain it relates to an infinite message loop between the popup and background processes in order to share the Vuex state but beyond that I’m not really sure of the specific cause; thankfully it happens in Firefox and Chrome so it’s reasonably likely to be something I’ve done wrong rather than a browser bug.
Assuming I can get that problem fixed, I may make an intermediate release that just loads up the existing “save” dialog from the new popup UI (as per the current state of that branch) but I wouldn’t expect it to take all that long to build a replacement for the dialog in comparison to all this preparatory work so perhaps I’ll bundle it all into the same release to avoid having both old and new interface styles at the same time.
I’d be happy for some help in the coming months but I think you’ll see from the branch that it’s a non-trivial piece of work so if you are only likely to have enough time to shift some buttons around, it might be better for you to save that effort until I have something more complete to then focus on testing and refinements of the new UI.