Thank you all for the very informative replies. I am talking to the owner soon to understand a bit more about this particular set up. He has singleshanded the boat from Sweden to Greece so it's not impossible. However if I need to slacken and re-tension the runners every time I tack then that's going to be a pain as I am planning to stay in the Med for the short/medium term then prep the boat for a circumnavigation within the next 7 years or so. From experience frequent tacking in confined channels around the Greek islands in lumpy seas in a Force 5 is not uncommon. So if the rig isn't a bit forgiving then I'll pass.
Whether you need to ease the runners on every tack depends on where the runners are, how well the boat points, and how full the mainsail is. On the aforementioned pre-war gaff cutter and 1975 Nicholson cutter/sloop I didn't and don't need to need to do so.