yeah, back to OP's Q and exec summary
D3 had the replacement hard crown, but shouldn't be needing to be replaced ever, has been changed to no longer have that. It has a captured O-ring for the turret, not beneficial for anything other than depressurized first stages, even then not relevant to this conversation. It's turret can swivel with hoses on it without hitting the DIN screw, not really relevant for most diving, certainly not recreational diving.
If you want the D3 buy in like the next 10 minutes before the price hike takes effect and the D3 regulators are no longer worth purchasing because the larger companies with more/better support will have cheaper prices. If you want to save money, the D1 is just as good for your use and the use of the vast majority of people and about half the price, just doesn't look as cool. For hose routing, singles tank routing with the turrets can be done one of 3 ways
Turret up, enviro seal down, hoses look like normal regulators, not a fan
Turret down but cocked slightly towards your left shoulder, primary on the 5th port going down, either as a 36" ish hose to an elbow, or a 7' long hose, secondary and inflator coming out of sides. Not a fan, but useful if you're diving in a drysuit in single tanks
Turret sideways, with primary and inflator on the turret, octo on the 5th port, SPG coming down. Gets the regulator flat, and allows me to swap from the left post regulator on my doubles to singles just by putting the primary on the same side of the turret as the inflator.
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