My very unscientific comparison:
While I had to look up some grammar points when I first started それでも歩は寄せてくる, now that we are into Volume 5, I almost never have to stop and look up grammar points, just the occasional vocab word.
On the other hand, I am still fairly regularly (once a chapter or so, on the high end) checking grammar in 五等分の花嫁. I also have to check vocabulary a lot more often (usually I get it from context, make a note, and look it up to confirm after finishing the chapter).
Itsuki and Nino are probably the worst offenders for grammar I have to look up, for different reasons. Itsuki speaks pretty much exclusively in keigo, and so uses a lot of formal terms and grammar that I haven’t seen much of (due more to what I have been using for immersion up to now), whereas Nino is the polar opposite. She speaks rudely, with a lot of casual and slangy speech, even more so than Urushi in それでも.
Miku tends to be the character who makes me look up a lot of expressions and vocabulary, because of her tendency to quote historical works. There has been a couple of times I’ve spent up to an hour researching a particular phrase because it’s archaic, thanks to her. So that would be something to watch out for.
Regarding the font, give me a bit, and I’ll see if I can pull up the page that has the multiple different fonts. It’s usually not to that extreme. I struggle the most with the curly/fancy font that makes an appearance sometimes, and some of the handwritten fonts.
There is also a particular font that makes 五つ子 look like 五っ子 instead, but that was just annoying the first time. Once you know of it, NBD.
Oh, one last note: the chapters vary a bit in text density. Some of them are incredibly text heavy, others are very light. That’s the other thing that made me lean BBC over ABBC; some of the chapters would be very difficult for absolute beginners to get through in a week, I think.