David, I went to Lanzarote last September and dived with
Rubicon Diving in Playa Blanca on the southern tip of the island. The centre was clean and well organised with good classrom facilities, a big kit storage/kitting up area changing room, showers etc. I took my own gear but the centres equipment, which was from a variety of manufacturers, appeared to be in good condition. They pump their own gas with nitrox at no extra charge. I used 15 litre cylinders and there was no extra charge for that either. Their affiliation is PADI/TDI and from talking to some of the guys there I know they do some technical stuff, rebreather courses etc. The instructors/DMs were a great bunch of guys and very helpful. The centre has two large rhibs with ladders and a hard boat on call for longer trips. I didn't see any sets of twins, but then I didn't look. I would imagine that they would fix you up if you were waving a few euros in their direction
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Sea temperature in January will be about 19 degrees (same as Tenerife), I was told that December/January is a good time to go as "that's when the big stuff comes in".
Rubicon Marina is a newish part of Playa Blanca and has grown out of a small fishing cove. It doesn't have all the hustle bustle of the other tourist resorts. The Marina area has a few good hotels but if you want nightclubs etc you need to go further up or down the coast.
Gareth
Disclaimer - I have no links with Rubicon Diving or Lanzarote, just went there on holiday and had a great time.