The advantage of a Strength-based magus is that it avoids some of the disadvantages of a Dexterity-based magus. The disadvantage is that it also misses out on the advantages of a Dexterity-based magus. This is tautological, but I introduce things this way because Strength is the default, and aside from being the default and therefore not requiring any investment, Strength has no real advantages for a magus. After all, a magus cannot use a two-handed weapon,1 which is the only real way to make Strength shine.
So then, the disadvantage of being Dexterity-based is that you have to expend character-creation resources in order to become Dexterity-based, i.e. take the Weapon Finesse feat. Once you have taken the Weapon Finesse feat, your weapon damage is poor, since you are doing this to dump Strength. Shocking grasp arguably says you don’t care, but if you do, that means you also take Dervish Dance,2 Fencing Grace,2 or Slashing Grace,2 or wield an agile weapon.
So the Dexterity-based magus is down a feat and a +1-enhancement equivalent on their weapon, or down two feats. Assuming you don’t lose your weapon, the weapon route is the better deal, but you would have to judge that risk yourself—and a bladebound magus, obnoxiously, wouldn’t have the option. What do you get for your expense?
You will be more accurate, and if you get Dexterity-to-damage, you will also deal more damage. That is, your Dexterity will be higher than your Strength would be on a Strength-based magus, because you can completely ignore Strength while a Strength-based magus really should have at least decent Dexterity. Without a two-handed weapon, Strength has no advantage to offset this benefit.
Your initiative is much improved. This is huge, because in most combats initiative will easily be the single most important roll you make. They will be decided primarily by who goes first. This becomes especially true at higher levels, where the game becomes increasingly rocket tag.3
You get substantially more AC, to the point that keeping your AC relevant becomes a meaningful, if expensive, option. Most characters at mid-to-high levels cannot afford enough AC to make it worthwhile, and should optimally end up basically ignoring it after the basic bonuses from a +1 armor. A Dexterity-focused character in light armor is just about the only exception.
Your skills will quite simply be better. Climb is worthless once you have flight—which you should—and Swim comes up rarely, if at all, in most campaigns. Meanwhile, Acrobatics and Stealth are two of the best skills in the game.
So, are all of those worth a feat or two? Generally speaking, yes, they are. Feats are very valuable, but that is a lot of benefit. There are not a lot of feats that could offer so much.
That said, there are also some really powerful feats out there. You will have to look at your build and decide if another feat or two could add even more than all of that.
There’s an argument that a magus can use a two-handed weapon—I’ve made it myself, here—but I’m largely going to ignore it on the basis of your request to avoid cheese. It doesn’t really change my conclusions, but it becomes harder to speak definitively in that case.
Unless you are forced to take Weapon Focus for something else, Dervish Dance is the best option here. No weapon option available to you is worth having to burn a feat on Weapon Focus for.
The game is actually most “rocket tag” at 1st level, but that’s irrelevant to the question.
