Mine (Pre-1984)
Post-1984
Notice the big black bar connecting the yokes in the top image. The reason I think this is an advantage is that it allows you to replace that big double arm bar with a single bar yoke, freeing up a bunch of room for the passenger on the copilot side. Here is what an awesome B55 cockpit looks like with a single arm yoke.
Notice how much easier it is to access the avionics on the right side and also gives more space. The disadvantage of course is that only the pilot can operate the elevator and ailerons, but in my 2+ years of owning this plane now I've never really needed that, including during instruction. Looking forward to more room, my only reservation is eventually teaching my sons, but I can always keep the dual control for later since my oldest is only 4. Or teach em proper in a citabria, see honey I DO need more than one airplane!
With this in mind I started looking for a single arm yoke to retrofit onto my plane. I found a few used ones, one for $600 and one for $300, but it was hard for me to assess their condition and I want one that looks new or almost new, so I ended up buying one for $1400 from Randy at Airmech (http://www.dualyoke.com/). This one is fully refurbed, powder coated with no scratches so it looks new, with a new chain all greased and ready to go.
In case anyone is wondering, Randy will take a dual on exchange and send you $1000 for the difference. I've decided to keep my dual yoke for now. Now I just need to install this sucker.