As a matter of interest, twin 175 Suzi rig combined wot fuel use about 120 ltr / hr for 48 kn on a 7.2m rig. No experience with a single 300 but twins use about around 105 each at wot. I'd suggest going for fly by wire on the twins so this will bump up the cost. At cruise of 23 kn on the 175's economy = 0.75 ltr / nm. The single 300 would be around 0.6 at a guess - a lot of fuel to make up the cost difference.
On the topic of warranty & support, while I've had no drama with suzi support at all, yammies are factory backed. Sometimes with warranty claims there's often more to the story too.
I'd go for the brand / supplier that can bolt the donk on & leave you to enjoy. Proven installs on the same tub as yours.
Enjoy the purchase.