I know
this isn't exactly what you're looking for, still going to suggest it. 4 ml is still ample size for juice. Yep, you might need to refill during a day if you use more.
The capacity aside I'd suggest this because it's an RBA. That means you can go spend -$8 and get yourself a spool of wire. You can wind up maybe 100 or so coils versus having to go scour shops for proprietary coil "assemblies".
You'll want to be looking for stuff you can use without being tied to particular hardware needs. With the postal ban/s going on and a nicotine tax looming it's clear vaping is taking on hard rounds of fire. If not tied to specifics you'll be in a better way to weather the storm.
I'm not trying to tell you what to do. Merely trying to offer some well thought advice/suggestion. And yes granted even this advice is opinion tainted, apologies for that, difficult to not interject. Take/leave it FWIW.