I have a Blacktip and a Genesis 2.1.
Even on lake and wreck dives, I have wanted more speed than what the Blacktip can do - and it can only even do that for a very short time.
Just one example: I dived the Jodrey, up in the Saint Lawrence River, with my BlackTip. The current was ... well, pretty normal for the SLR. At the end, I was doing my deco going up the side of the island that the Jodrey is laying against. I had to go against the current to get back to the boat.
Long story short: The BlackTip gave me two options: Actually move against the current, but only a very short way at a time before it got too hot and shut off. Or, hold my position against the current using a gear that it could maintain for an extended period.
I haven't taken it there yet, but I am completely confident that, had I had it then, my Genesis would have towed me back to the boat speedily and without breaking a (figurative) sweat.
Your BlackTip may have had enough thrust for you, for the dives you have used it for, so far. But, a more capable scooter would let you safely dive in more challenging conditions. (and, of course, no scooter relieves you from planning for the possibility of it dying - but having two does...
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... way too expensive.... for YOU and your opinion and/or wallet.
Lastly, just being frank (but don't CALL me Frank! lol), I think you have been lucky, so far, with your BlackTip. My gut feeling is that they are not just less reliable than a Genesis/Seacraft/Suex. I think they are an order of magnitude less reliable. Which is just my way of trying to say they are not just a bit less reliable as a cost compromise. I think they are fundamentally less reliable - at least, when using power tool batteries - in a way that, because of my experience with mine, means I simply would not use it for some dives where I would use my Genesis, even though the depth, thrust, and runtime required are well within what the BlackTip can do.
And, really, at this point, there are enough high-quality scooters that can be charged without opening their hull that I wouldn't use any scooter that couldn't for any kind of "big" dive. But, that's me and my personal preference. If the dive were within the limits of depth, thrust, and burntime of a Go!, I would totally take one of those over a Suex, for example.