Different types of teleportation? Different risks? This is a banned knowledge in the White Council and may be for a number of reasons.
1. It is lethal
2. It is difficult
3. It breaks one or more the laws of magic.
Classically teleportation actually invokes the destruction of the test subject and their reification in another place, essentially death and rebirth, a classic breach of the Fifth Law, meaning it’s both points 1 and 2. This may only have been realised some time AFTER it became known, leading to it’s proscription, after the formulation of the Laws. Point 2 was relevant at that point it probably required a powerful practioner, could end badly, be blocked easily by counterspells etc. The knowledge would have been lost at the practitioner level over time relegated to the library. Drakul must really have been annoyed that River Shoulders was an opponent old enough to know countermeasures. Same with Namshiel, he was old enough to know countermeasures to the countermeasures and it must have required considerable focus by him and Marcone to avoid it going badly against the Titan.
Harry made the escape potion in SF that was half speed, half teleportation. He didn't seem concerned about it being illegal. Or at least not that I recall.
I won't speculate on danger or difficulty, because Bob is beyond average wisdom and would negate a lot of concern there. But I'll point out that the phrasing Harry uses, "Is this the super speed one, or the teleportation one?", seems to imply that he's done both before.
I agree that most proposed methods of teleportation seem to skirt a law being broken. But only for sticklers like Morgan looking for an excuse.
Personally I like the idea of folding reality between two points to move between them. Like Harry describes Drakul as disappearing like behind a telephone pole. Just warping reality so that two non-congruent points are touching via magic, but without a visible doorway or portal.
I don't think that's what Drakul did, unless River's counter managed to unwarp reality. And Marcone's technique seemed to involve the hand pointing at the destination, which is more like movement than warping. Like he's physically representing his intention to "stop there".