I started out scrolling with spiral blades more than 20 years ago. I cut free standing tree puzzles out of 1 1/2 red oak with spirals. Many fret work patterns, Christmas sleighs, etc. I stopped scrolling for several years when I began doing stained glass projects. I was recently widowed and decided I needed to get back to scrolling. I bought a Dewalt and decided it was time to learn to use flat blades. I feel much like people who are learning to use spiral blades. I struggle to slow down with the flat blades and find I sometimes feel like a runaway car heading down hill at breakneck speed. The flats cut so much faster and require far less force to cut IMO. They do leave a much cleaner cut and sharper corners.
They funny thing is, I watched a youtube video by Charles Dearing (sort of a hero of mine), and he also finds flat blades harder to control than spirals. I'm starting to enjoy the flat blades but, with the advent of new spirals and reverse spirals and flat end spirals, I can see the value of both styles.
I use a small needle nose pliers to slightly flatten the ends of my spiral blades. I simply put the first 3/8 to 1/2 inch of the l blade into the pliers and squeeze them closed to straighten them a bit. I also pay attention to the feel of the clamps when tightening them to avoid turning the ends into "hockey sticks" (the annoying bend in the blade end that will increase the possibility for breakage.) I've found that over tightening will often bend the blade end.