the theory is, for *commercial* production, 30" is about the maximum width that allows you to a. walk/jump over the beds to quickly navigate the garden b. access the rows from both sides for transplanting, harvesting and weeding, it isn't "too far" for most average people to reach everything in the row from either side. The advantage of having as wide a row as is practical to work by hand is that you have more garden and less walkway space.
If i were you I'd standardize on a width compatible with both your power harrow and flail. Obviously if you aren't concerned with a little inefficiency, a 26" flail can work on a 30" bed if you make two passes, or one pass if it's a single row down the middle crop like summer squash or tomatoes etc. If you aren't trying to make money then I don't see why everything needs to be running at max efficiency. Actually 26" beds should be even easier to work with using hand tools than 30", it's just slightly less efficient for crop space. If you're just gardening for your family you'll never have any problems, heck I'm gardening on 1/3rd an acre and we still have big surpluses of many crops, it's frightening how productive well managed gardens can be.
The fairly significant advantage of the power harrow is that it damages soil structure less and doesn't bring up new weed seeds, it's just stirring what material and seeds are already there in the depth of worked soil that is set on the tool. AND it makes nicely packed, flat, perfectly groomed beds which are very important for precise seeding using push type garden seeders. For me that's radishes, beets, carrots, corn, peas and beans, pretty much all other crops I transplant in to gain extra season time by starting them in greenhouse, and to ensure 100 percent of the row space will be occupied by plants (when you seed you never know exactly what you're gonna get coming up)