The funny thing about milestones, from my own experience, is that xp or milestones don't really make a whole lot of different. The party levels up at exactly the same rate. I mean, look at this thread, most of us can ballpark how many sessions it's going to take to hit level 4 before play has even begun.
Sure, we might be off by a session or two either way, but, by and large, you know your group and you know how you play. I remember years ago running the World's Largest Dungeon and I was doing xp tracking. Then, I went back over my notes and realized that I could just level the party up every X sessions.
So, I tracked it for a couple of levels - made an estimate when they leveled up as to when they would level up the next time and it turned out that my estimates were pretty much spot on. The party still leveled up pretty much on schedule. That's when I largely dumped XP and just went milestone. It really doesn't make any difference and it saves a bunch of futzing about with tracking XP.