Solo-Mid vs. Solo Off-Lane for Magnus

Mag offlane is legit, although there are good reasons (outlined by many here) why you tend to play him mid instead. That Blink Dagger is absolutely core on him, and a pair of Arcane Boots is very helpful too for a hero with inexpensive spells but a small mana pool.

He's tanky, has a farming and escape skill - that's legit for offlane, but he does suffer more than some others and finds it harder to recover.

I especially like him with a Crystal Maiden on the team - that mana tick is great when your main farming spell is locked at 80 mana, and it gets painful pretty fast for a melee enemy carry. Other alternative is to run him with a KOTL - trading hits with that is not fun :).

Again though, suffers a bit more than some other offlaners - Slark especially can be a nightmare as Skewer doesn't break his leash.

Generally I'd pick him with mid in mind, but then shift him offlane if it's going to be horrible for him or something else fits your plan better.

I play Magnus a lot. I prefer him mid, as he can fill the position best. Mag is one of those heroes who can fill most spots however running him a pos. 5 is not the best idea, I have tried it and he is too squishy being under leveled and without a blink until minute 20.

Magnus Offlane is pretty good.

-He has the ability to use Shockwave stopping the wave from pushing, as well as harassing the enemy carry, causing them to back off. Magnus can then Skewer, and shockwave killing them, if they stay in lane last hitting.

-Getting a Blink Dagger is a bigger challenge due to the fact that you can't use auto attack to last hit that often, and you don't have the huge rune control that you normally would have mid, having less mana to uspam shockwave.

-Mag has little, to no gank potential. A solo offlaner is playing for the mid-late game. he has almost no early game presence, because of the fact that without a blink dagger magnus cant do a whole lot.

Magnus is in my opinion one of the best mids.

-In a 1v1 matchup, magnus will almost always win. the only heroes I have ever had trouble with, was a skywrath, OD, and Puck. Mag has a fairly large base damage in the early game, making lhing and denying pretty easy. you can also use Shockwave to last hit and harrass, far better than you could in the offlane.

-Mag can spam Shochwave much more often now that he has rune control. after pushing the wave with shockwave, he can secure a rune with often no trouble. Ganking is an option at level 6, with or without a blink dagger. If you were to Get a haste rune, you could gank at level 4 or even level 3.
(I wrote this super quickly, so sorry for any mistakes I made.)
-Mag has amazing early game presence, ganking, getting solo kills, defending towers, farming. getting a quick bottle, and brown boots. (I often get a bracer too) and then rushing a blink dagger. Magnus can get a double kill for himself, or his carry. at minute 11-15.