Though very popular in the UK and France due to the extreme tidal range these yachts are not common here in Australia. Most here are one off custom yachts like Warlock.
A properly designed Twin Keeler will sail as well as a Single Keeled Yacht with the added advantage of allowing to dry out on the beach. The are very resistant to rolling around at anchor and resist rhythmic rolling when sailing down wind.
Some Bilge Keelers (as opposed to Twin Keelers) do not tack well and perform poorly to windward so a Twin Keeler would be my choice if sailing quality is important.
Lord Rivendale in the 1920s researched twin keel yacht design and built some very successful yachts. There is a lot of info online for those interested. Lord Rivendale's Bluebird of Thorn is pictured above. Built in the late 1930s she is still sailing in UK waters.