My wife Erin likes her coffee brewed exclusively with an Aeropress. Sometimes I'll go Aeropress, sometimes espresso, and when preparing for a hot day at the markets I might be brewing a big batch of nitro cold drip. So that means up to 3 different grind sizes in any week.
Before I continue I want to be clear that the products mentioned in this post are included only because it's what I actually use. I'm not selling them, I'm not getting paid for this post and there are no affiliate links.
Our main coffee grinder is a wicked Quamar Q50 S. It cost an arm and a leg but is worth it. It is a stepped grinder, which is good for when you switch between different grind sizes often.
My second grinder is a modified Porlex hand grinder. These are the bees knees of hand grinders. Adjustable ceramic burrs, made in Japan, stainless steel, no glass, they are bombproof. The modification I have made is to use it with a 3D printed drill bit, purchased from Shapeways, so that I can use a drill to operate it and save my huge muscles from getting any bigger. I have had people tell me this is a bad idea because the coffee will get hot when it is ground. This is rubbish, the burrs are ceramic and it's only 14 grams of coffee. All you need to do is touch the burrs and coffee afterwards and you can feel nothing is getting remotely hot. No doubt someone once said it on a forum and since then the echo chamber of the internet has turned it into a fact. It is a useful lie to help sell more expensive grinders.
The advantages of the Quamar is it's way quieter, will grind super fine and is more convenient (there is a bit of stuffing around with the modified hand grinder). The advantage of the Porlex is that I can grind a single shot without leaving any beans (and barely any grinds) behind. This means that I can switch coffees without having to stuff around with removing hoppers, emptying chambers, etc, etc. All I need to do is put a different bean in and grind. This is great because I like to taste lots of different coffees side by side to fine tune what is working and what isn't. That's where the Porlex is so good.
Then there is the advantage of having both, with one set for espresso and another switching between Aeropress and Cold Drip.
Now for the 'Flair' part. I make my espresso with a manual lever pull gadget called the Flair. It's a brilliant invention, but the main thing I like about it is the lever allows you to adjust the pressure (during the pour) as needed. This means you don't need to dial in for every different coffee.
Let's say you are comparing two coffees and one is roasted a bit darker than the other. If you have a fixed amount of pressure you will need to fine tune the grind to get the best extraction for each bean separately. This is a pain and you'll waste a lot of coffee over time. Instead, a coffee machine that allows you to vary the pressure is more forgiving on grind size. So you can grind two different beans on the same setting and then tweak the pressure to get a great extraction from both beans. Sure, there may be differences in flavour due to slightly different pressures, in theory, but I'd challenge anyone to consistently triangulate them in a real-world setting.
So if you want to drink two espressos, using different beans, at the same time each morning then one good option is to pair a Porlex and a Flair.