You may be unpleasantly surprised. I have TWSBI Eco-T pens in both <M> and <F>, which write similarly to some Japanese <B> and <M> nibs respectively. I would recommend, if you want something with true portion control, to get a Pilot Prera in <F> or a Kakuno in <EF> (or any pen with a Japanese nib), just to check it out. Both are fairly affordable.

Also, given you’re a lefty, you may want to avoid “good paper” for fountain pens. Coatings on the paper that allow inks to “sit on top” of the page while they dry, preventing feathering and allowing the ink’s properties to develop, understandably slow the drying process. In addition, avoid Noodler’s inks. They look beautiful but dry at an absolutely glacial pace—in my experience, up to several days’ time to fully dry (unassisted, in a dry environment) on Midori MD notebook paper.

I’ve used an ECO and while it’s not my favorite pen, I have nothing bad to say about the nib (I believe mine was a fine as well). The way FP’s write can vary dramatically between different inks though. I’d recommend first trying out the ink you have and seeing what about it you don’t like before researching other inks.

Just asking out of precaution, but are you sure this bottled ink of yours can be used with fountain pens? Even if it is, it’s best to be careful with a fine nib (I’ve learned the hard way).