As I've said on this forum before, there are people who do flights like this all the time without fanfare for a living.
Cliff Taits flights just show what can and has been done without the backup aircraft beside you
Before we get to wrapped up in this latest flight Google Flt Lt David Cyster who did the same flight SOLO in a Tiger Moth in the 70's
Having done this route twice 1993 and 2013 apart from some idoscricities in a few countries aviation has progress where every country has the same procedures, and all the problems with clearances are fix by using people such as Universal or White rose.
Notwithstanding I don't think I'd like to spend some 150 hours in the cockpit of a biplane without an autopilot, and certainly not at 1500 feet AGL (think engine failure)