Could be that a few searches could answer your questions? The answer you want is a little vague but I can try.
PTO: the 406 Unimog has external PTO available, front and/or rear, either 540 speed, or 540 plus 1000 rpm depending on the model PTO attached to the side of the transmission. The FLU-419 has no PTO except one used to drive the hydraulic pump. Not usable for an implement.
Hydraulics; 406 mogs typically have a front system used on the front loader (or whatever implement you run on the front. DITTO the FLU-419, however the 419 is not set up to add "whatever" to the front, just the Schmidt loader. Of course other implements could be adapted. The 419 has the same front pump but a different reservoir and plumbing setup.
406's can have other hydraulic systems too, typically a transmission bottom-mounted PTO driving a hydraulic pump, or a side mount PTO off the cascade housing. Depending on the spool/multi-valve setup (typically on the implement, not on the 406) this system can be used on the back-hoe, rear mower, etc. Note that the 406 has a three point mechanical attachment available, both the Case model and the German 'Ag Spec' model. So the 406 will accept whatever 3-point implements you desire and has PTO and/or hydraulic quick-connects to run them, just like a well-equipped tractor.
The FLU-419 has a control system (spool) for the back-hoe, but it is not intended to run anything else on the back, like 3-point implements. You can run hand tools off that system and the reel of hose is there for that purpose. There is no 3-point setup for the FLU. You are on your own if you want to attach anything except the Case 580-derrived back-hoe. The interface matches nothing else that I know of.
the 406 mogs have several transmission and clutch options, starting with a single clutch and 6 speed transmission (with either a 1-2, 3-4-5-6 shift pattern, or a 2x4 shift plate with two ranges of 4 gears). The FLU-419 has the 2x4 system but with air shift between ranges, I think. Someone please correct me on any of this.
A 406 can have a 'cascade' reduction gear set ahead of the 6 speed, with 3 more ranges. Therefore a well equipped 406 will have 24 forwards theoretically, with four locked out, so it's a 20 speed. That model often has a dual clutch to allow 'live' PTO driven implements.
No options on the 419 transmission.
Your question is not a simple one. Bottom line, in my opinion, The FLU-419 is great at what it does but is not as versatile as a 406 Unimog.
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