If you were to ask any longtime fan of Thomas what their thoughts were on the new original characters that were created for 'All Engines Go' as a whole, they would more often than not tell you that Kana started out surrounded by a bout of controversy but soon had a lot of fans warming up to her when she finally got her chance to shine. Sandy, on the other hand, with how her character was written during the first season of the reboot was still wallowing in the mud of a controversy of her own. Not that she's a bad character or anything, far from it actually since she weirdly fits in from an aesthetic standpoint much like Kana did as we've never had a rail speeder type of character in the world of 'Thomas & Friends' before. But in terms of personality from what we've seen so far, there's nothing really that special about Sandy since she's the typical 'full of potential but has a lot of growing to do' type of character who doesn't like the protection she gets from those who are only looking out for her - if anything, she reminds me a lot of Apple Bloom from the first four or five seasons of 'My Little Pony: Friendship Is Magic' who went through a similar character arc. So while Sandy may not be that interesting of a character, she's not as bad as some people have made her out to be. And hey, at least that big thing about Sandy being Carly's daughter was put to rest by the production team, because that just raises questions I don't want the answer to.
But with all of this in mind in regards to my thoughts on Sandy as a character and now that we've had more than enough time in order to cool down before we started talking about this current season, it was only a matter of time before Sandy would step back into a lead role again and...if you've read or seen any adaptation of the classic Aesop fable "The Tortoise and the Hare" in media, including all of the ones from the world of Thomas, then you've pretty much already seen this episode before it even starts.
I think it goes without saying that "Speedster Sandy" is pretty much just All Engines Go's answer to Jack and the Pack's "The Tortoise and the Hare" as well as Season 8's "Edward The Great" and even the iconic Random House book "Catch Me, Catch Me!" which will definitely turn fans away from watching this episode as if they weren't turned away from All Engines Go before now. That being said however, there are some differences between these four versions of the classic fable as both Thomas in "Catch Me, Catch Me!" and Sandy in "Speedster Sandy" use their size and small stature to get ahead in their racing environment and win whereas "The Tortoise and the Hare" and "Edward the Great" were just straightforward adaptations of the fable and not to mention that Kana seems to be the only one of the four racers who doesn't act like a spoilsport about losing the race to their competitors.
But overall, just having a few changes here and there doesn't change the fact that "Speedster Sandy" is just another adaptation of a classic Aesop fable to add to the pile that doesn't do anything to stand out from three adaptations that came before and were far superior. But even at that, I'm going to be nice and give a 2.5/5.