My question is, is this too far out as a space travel alternative?
Too far out? How could an excuse to say "Without precise calculations we could fly right through a star or bounce too close to a supernova and that'd end your trip real quick, wouldn't it?" be too far out?
Granted, you're talking about instantaneous teleportation rather than superluminal flight through hyperspace, but, still, it sounds like pretty mainstream FTL trappings to me.
I've often wondered why there's usually only one method of FTL in most settings. I think it's be neat if different races/factions had different methods of FTL. Like a race with Stargates, another with Fold tech, and a third uses Hyperdrive. Give each method benefits and drawbacks to balance them out.
That's one of the things I really liked about the (computer) conquer-the-galaxy game
Sword of the Stars. They had six races/factions (I believe seven with all expansions) and each one had its own distinct method of FTL travel, with different tradeoffs for speed, flexibility, etc.
Mongoose Traveller 1st edition had a page with three or four alternate FTL methods (aside from the Traveller default of one-week jump drives), but the assumption seemed to be that you'd just pick one for your game, not use all of them in the same setting.
Suggestion: if you're trying to come up with an "explanation" in order to make your world building more, let's say, "plausible" or "realistic", than make sure it doesn't have anything that obviously sounds implausible by going against facts we know to be true. Faster-than-light travel, teleportation... whatever goes. It might not exist in real life, but it's sci-fi, so the reader or player will be willing to buy it. However, when your explanation includes the statement that "the probability of porting into a solid object is high if you don't spend the necessary time doing the calculations", that's much harder to sell, since it goes against established facts that we do know.
Going by this particular estimate, only 0.0000000000000000000042% of the universe's total volume is occupied by matter. But even if someone doesn't know that specifically, any casual sci-fi fan will be aware that space is, in fact, vastly and mind-boggingly empty with only tiny collections of matter located very, very far from each other. So, in fact, the chances teleporting into a solid object should be very, VERY low.
Even so, I don't have any issue with the OP's description because you're not going to be teleporting to an arbitrary random point anywhere in the universe. If you're going someplace worth making the trip, then you probably want to arrive somewhere in the general vicinity of a substantial quantity of matter. As long as the error in your arrival point isn't more than a few thousand km, then there's a non-negligible chance of arriving at a location which intersects the substantial quantity of matter you had intended to visit.
However, that said, this intersects with the recent "TPK for one character's mistake" thread. After one or two incidents of ships misjumping into planets and causing massive civilian casualties, FTL will very quickly be either banned or restricted to only arrivals far enough out in space to ensure that you don't arrive in the space occupied by anything of consequence, purely for the sake of keeping planetary populations safe, even if interstellar travelers are willing to accept that risk for themselves.