Just my opinion, but...
If you want a retention system clipless is better by a significant factor. For clips and straps to do any good they need to be tightened and then they are harder to get out of than clipless while also being less comfortable. I started biking long before clipless was readily available and found it a great change over clips and straps. I gladly embraced the new technology and never looked back

BTW, those little half clips with no straps are pretty much totally worthless in my estimation. Some folks like them though. I never tried power grip straps, but I can see where they might be a good compromise for some riders

How important having a retention system is will vary widely depending on the rider's preferences and the tour. For example, if they will be riding most of their waking hours, then bikes shoes with clipless retention will probably be way more of a plus than a minus. If on the other hand they will be hiking or sightseeing as much as riding then some trail runners become a big plus. In either case I like having clipless pedals and nice bike shoes, but I can see where others would differ. If the tour is expected to have a lot of hiking that is more than a few miles at a time or over especially challenging terrain, I also take some trail runners. I have been know to just buy some trail runners for one part of a tour and would consider mailing them home. I did that when we decided to spend a week in Yosemite hiking and sightseeing before continuing the tour.