The longer, the less safe, obviously (not just because of breakage, but also because of handling, the involved forces, and simply because there's a much longer blade protruding).
But if you respect them for what they are, and use them accordingly, they are pretty safe.
You will normally not want to use the full length of the blade. Except, you could maybe use it that way in a router table, but then you have to go very shallow. That is not the intended purpose of the bit, though. you are not milling a thickness foam.
The "normal" use of these long bits is in a plunge router for a diversity of joints. But the bit is not intended to cut that depth in one pass.
Neither is your router powerful enough, nor would you be strong enough to safely hold The BEAST bit if you plunged in full-depth. That's DANGEROUS.
For the normal length bits, usually does at least two, more commonly three passes. With a long flute bit, usually do at least 8, if not 10 passes.
SpeTool Extra Long Series bits link: SpeTool Extra Long Series Woodworking Router Bits (spetools.com)
