I would use multiple classic chargers, given I have two 6D and now bought R6/2, I can charge 3 batteries simultaneously. At least this repeated "BP-511" scenario is nice and I can use whichever of those batteries in whichever FF camera I have.
Not sure how fast it is, but I've been using several Manfrotto ProCUBE Professional Twin Chargers for years for my R5 camera batteries and the units work quite well. As an added bonus, there is a display on the front of the device that indicates the charge level of each battery.
This may not be the fastest dual charger, but it's what I've found to be the ultimate dual travel charger. These things are absolute featherweight and two of them are smaller/lighter than one canon brick. I was hesitant to use them for travel because they're so light they seem "empty" but they've been workhorses for a long time now.
I have not yet found a rapid charger for the LP-E6 type battery (but also have not looked extensively). B&H lists a ton of charger options, but again, none appear to be overly fast.
This one they have listed from SmallRig for $11 appears to be the same one I received with my Neewer LP-E6NH batteries, and have used for the past year, in addition to the official one from Canon. So far it has worked well, but I wouldn't consider it to be a 'rapid' charger. It's probably fastest when only one battery is being charged.
Unfortunately the likely solution will be to buy a sufficient quantity of batteries to last you a typical day, along with the corresponding number of chargers in order to have them all ready for when you next need them.
I do like having some chargers that work from USB so that charging can be done in the field from a power bank.
They both seem to work equally well. One stays at home, the other travels with me. You need USB-C charging bricks for both. A single battery will charge faster but I just leave two in over night.
