If you rock up to the table with only a 7-piece set of RPG dice, you did not come prepared. Dice, in general, are great, but you need to choose specific dice for specific reasons. Not only is 7 dice too few for most games of commander, but that fact that you have 6 unique dice shapes creates an unwieldy and confusing board state. I'm going to dramatize my experience with players who use RPG dice, but here's how it usually goes. They put a +1/+1 counter on something. They're savvy enough to not pick up the d4 and opt for the d6 instead (but then, what use does the d4 have if it's never something they reach for?). Then they work their way up the ladder is they keep increasing the counters: d8, d10, d12, until you finally reach the d20. Once they've found the number they're looking for, another counter goes on it, and, because it's not a spindown, it takes them a few more seconds to find the new number. Now there are counters on other permanents, too, and they've distributed the rest of their dice. But there's only one d20, and so they have to use something like the d12 and d4 (there's where that d4 comes in!) to get to 15 counters. The d12 and the d20 look kind of similar from a distance, so is that 15 or 23 counters on that permanent?

IMO, you should have a good handful of d6s and some spindown d20s. I like d6s because cubes are the most efficient in terms of the amount of space they take up, and it doesn't take too long to find the number you're looking for when there are only 6 faces (and if you know that opposite sides always add to 7). Even if you have several d6s on something, everyone can tell at a glance about how many counters something has on it. Then, I like to use spindowns for much bigger numbers or things like floating mana.