Tenggol is sweet. If you are in Malaysia I'd definitely say go for it. I dont think id fly around the worl just for it. ..Its a bit of a mission, 4 hr drive from KL and then a 45 min speedboat ride to the island. We stayed at Tenggol island beach resort, the other one on the right hand side is tenggol coral beach resort. And I think the one to the left is haunted haha. I was there with students, so we were diving on our own, i am not sure how it works with diving there as a guest (most people are from KL and go with instructors or at least DMs). There are some cool dives, there is a little pinnacle out crop with a little lighthouse off the main island that is very beautiful when the vis is 20-30m. There are a couple wrecks too and at the end of the season you have a chance of seeing whale sharks.
Another island that is nearby that does not have as nice diving, but a little more comforts is lang tengah, if you We stayed at a resort, before it was transformed into a snorkeling hub for foreign tourists, not sure if they have diving there anymore but a few of the places on land tengah do have dive operations. There where leopards sharks, but think they were fished out.