I caught this last week on the German 3rd / regional channel RBB, unaccountably included on a Spanish hotel cable TV service. Unfortunately for me, with a lot of work to do the following day, I couldn't bear to turn it off, so got to bed rather late. Why? Because as most of the other reviewers have noted, it's really rather good. The action just keeps flowing and the entirely watchable cast imbue the whole thing with a decent slickness.
Spanish director Antonio Isasi-Isasmendi captured the emerging glamour/spy zeitgeist with style, underpinned with a workmanlike eye for detail (I forgive him the wrecked car replacements, I'm sure the budget was not over generous). The occasional asides of the Tony Mecenas hero are fine in the context of the time and probably soften the otherwise implausibly super-human aspects of the character. It's a technique already pioneered in similar genres, e.g. Roger Moore's "The Saint".
Mid-sixties Istanbul comes across as very Euro-Mediterranean and serves as an excellent backdrop for most of the action. The plot was a satisfying mix of set pieces (meaning that one felt at home with the genre) and unexpected twists (meaning that there was no way the viewer could foresee the eventual outcome). Like a number of other reviewers, I also found the relatively low profile of Sylva Koscina for much of the action to be a bit of a shame, having fallen for her somewhat after watching the excellent "Deadlier Than The Male" recently.
P.S. Retro-discovering these decently constructed sixties Euro-thrillers, particularly those made totally outside the Anglo-American sphere, has become a real pleasure in recent years.