I have been to Koh Lipe a few times. I went diving with the dive operation at Lipe Resort. Horrible experience. Equipment not properly maintain. The owner came to our hut and offer us some drugs. When we refused, he insulted us for not having enough "balls" to take a hit?!! We just finished diving 4 hours ago and don't feel like taking and drugs.
He walked around the island stoned from the drug most of the time. WHile we were at his shop, he got into a fight with a customer, throw his beer bottle at his employee(dive guide) and fire her on the spot. fOR YOUR SAFETY AND ENJOYMENT OF THE ISLAND, STAY AWAY FROM LIPE RESORT DIVE SHOP!!
Koh Lipe is a great place to chill. If you walked 15 min cross to the other side of the island, you can swim with sharks! I made some friends with the local fishermen and went fishing with them. Mostly spear fishing, then we sell the fish at the restaurant at night.
It is a good idea to hire a boat for 800-1000TB for island hopping tour. If you free dive, you will enjoy it more than scuba.
No, Koh Tarutao is not similar ti Similan. Not even close. It is not necessary to go to Koh Tarutao for diving. Not much going on there.
To get to Koh Lipe, you can take ferry from Satun(Thai) or pakbara(Thai). I prefer Satun for shorter ride. You can also take a ferry from Langkawi Island(Malaysia) to Koh Lipe, but you have to stop at Koh Tarutao for a brief immegration stop.
Check out this web site for more info.
http://www.stgt.com/sabye/maps.htm
Enjoy!