From what I've heard and comparisons she sounds noticeably weaker and younger than her previous iterations she is also choppier than her v2 and v4 but she is compatible for xsy with v4 I would personally say I wouldn't bother with it because of those reasons but
I didn't know that Luka SP could xsy with v4, very interesting. If she sound choppy as you mention then i don't think it's a good idea to switch to Luka SP since, i have enough trouble working with Luka v4. Also there is possibility to use Luka SP doing cross-synth with V4 version to explore the new potential in her voice.
At first i thought Crypton actually do something to improve her Quality of Life and fixing constant glitches and warp audio noise. It's seem that is not the case.
Just from listening, she sounds like Miku unless she is tuned well, and she doesn’t sound as I guess strong as @BiscuitsandTriscuits also said. I’d say probably more of an alternative for a more “cutesy” sounding voicebank.
I am aware that people compare her to miku because she do sound like miku (some people call her Hatsune Luka lol), some say that she may use a samples that recycled from miku recording. To be honest, i can't blame them.
This is my personal opinion that base on my experience with Luka. I don't think she have anything to do with miku and yes, Luka SP sound like miku but to my ears, Luka SP do not share samples with miku at all (i believe) due to the different between fundamental frequency of Luka SP compared to miku.
I might be wrong, my ears is not a reliable analysis tool.. Unless someone willing to do a depth fourier analysis for this...
Anyway, she is sound cute though, even it's not my cup of tea.