I'll throw my experiences in here.
I've been a fan of MOI TaylorMade putters for a while, back to their huge spiders with half ball alignment aids, the spider blade with the two tone paint, the DJ/Day spiders, etc..
I'm a fan of putter makers who try different ways to make the game easier for us.
I enjoyed the original Spider line, I preferred the Day model over the DJ model because it was a touch softer.
For me, the lack of alignment line proved to be a pain, as I was very line dependent back then.
When the SpiderX came out, I immediately wanted it because it looked more compact.
Last July I ordered a MySpiderX, with the flow neck.

I am not a face balanced putter fan, so it was either slant neck or flow neck for me.
I don't mind the slant neck version at all, as I currently have a Chalk slant neck that I really enjoy putting with.
The only issue with the MySpiderX I originally ordered was I ordered it without any line, hoping the white track would be enough to align. The other problem was I ordered one of the color inserts that was firmer than the retail model, and hated the feel.
I am not a fan of the full sightline, as it is so long it was a pain to make sure it is lined up properly.
So this time around, I practically ordered the exact same putter but with a short T sightline as it creates the illusion of the width and sightline of a traditional anser variant shape. Also went white face to keep the soft feel.
For me, I love the roll the SpiderX puts on the ball. I agree with the others that it rolls the ball a touch further than a traditional non groove blade in my experience.
My putting goes awry when I am on slow greens and try to hit putts instead of roll them, so I love using this on slower greens.
On fast greens, my Cameron is still my goto.
One of the things I was worried about with a Spider is that I would never want to go back to a blade putter again.
I've tried the Squareback 2 and other widebodied putters that I felt would be similar to my timeless but with a little extra forgiveness but with mediocre results. Also, using those putters made the Timeless feel too foreign for some reason.
But with the SpiderX, interestingly enough, I can go back and forth between putters and feel fine. If anything, applying the same kind of carefree stroke on the blade than I do when I putt with the Spider re-affirmed that it's the Indian not the arrow. I putt with equal confidence with both the Timeless and the SpiderX.
I'm currently using a slant chalk SpiderX and absolutely love it, with a flow neck SpiderX in silver on it's way. I can use the slant or flow neck interchangeably, just prefer the way the flow neck frames the ball at address more.
The best part about getting a Spider is now you have another excuse to get a whole bunch of covers, you can buy both blade and mallet covers hahahaha.