When people come on and advocate for a 250 as the only reasonable starter bike I won’t respond. I don’t particularly agree but I understand the sentiment. However, to argue for an SV650 and against a Shiver is a little different. The Shiver may be a little more powerful but essentially you are looking at two similar machines. Mid sized V twins with very linear throttle response. If you treat the throttle with the proper respect, which is vital on either an SV650 or a Shiver as a learner, I don’t think those extra horses will come into play. Granted if you get stupid the Aprillia will let you get a little stupider than the Suzuki. However, my guess is that running the Shiver in Rain mode would make it very similar in performance to an SV. Would it take it down to a 250 level? No. Will it make it shed 50 lbs or a few inches of seat height? Of course not and that’s why I won’t argue with anyone about starting on a 250. However, if you’re all right with an SV 650 I don’t think there’s enough difference from the Shiver, especially in the lowest performance mode, to recommend against it.
To the OP, if you could pick up a new Shiver for $6K I’d say jump on it. Then treat it with respect, it can kill you(but so can a Ninja 250) and take the time to learn to ride properly; learning doesn’t end with a passed BRC. If you drop it, pick it up, assess the damage knowing that’s the chance you took by buying a new Aprillia as your first bike.