It’s a gun, with some sort of building attached to it.
If you’re thinking of getting the SU-100Y for any reason other than the gun, forget it. This tank is a gun and nothing else. It performs poorly in literally every single aspect that is not the massive gun. It has mediocre view range, radio range, speed, mobility and armor.
Excuse me, did I say armor? The SU-100Y is made entirely out of bubble gum wrapper held together by positive thoughts from the crew. With a 60mm all around armor, you’ll be lucky to get even a single bounce. The mantlet is pretty strong, but as you have so much SU-100Y around it, getting hit there is a rare event. Depending on the distance, the upper frontal plate can also bounce a few shots, which will leave your enemies yelling in disbelief at their monitor. Still, since this lumbering suburban housing unit doesn't have preferential matchmaking, you will often find tier 8 tanks more than willing to take some HP off your hands.
At 350m view range, you won’t do any passive scouting, not that it would matter, since you have about the same camo rating as a 2 story house (and about the same size too). You are one big, fat, easy target. Drive with support at all times. You won’t be able to turn fast enough if someone decides to circle you, and pretty much any tier 4 tanks (and tiers 3 and 2 if using gold rounds) can penetrate your armor. If you decide to try your hand at some assaulting, you will find that the horrible gun arc means you often feel like someone with a stiff neck having to turn around to greet an old friend. Except instead of "hi", you greet them with pain.
And since we're talking about pain, let’s talk about the pro, as in, the only pro and the thing that single-handedly made this tank worth buying: The gun.
You won’t find a gun like this in any other tank at tier 6. You simply won’t. This thing has a massive tier 8 130mm pipe sticking out the front, capable of dealing death before the enemy knows what hit them. It has an average of 196mm of penetration and an earth-shattering 440 average damage, with an accuracy that is not that bad at all, at 0.38 m. The one thing stopping you from going full Rambo and blowing up the entire battlefield is the glacial reload time. This gun has a rate of fire of only 3.75 rounds / minute, putting it nearly on par with the BL-10 on the ISU-152. In fact, the SU-100Y is the ISU-152 of the tier 6: Massively overpowered gun for its tier and pretty much crap in everything else.
Is it worth my hard-earned cash?
Well, unfortunately I can’t give you a straightforward answer. If you’re used to playing with tanks that can’t take a hit but can hit like there’s no tomorrow, you’ll be right at home (literally) on the SU-100Y. I’ve had tons of fun punching off 3/4 of the HP of most tanks I meet that I’ve had nearly uncontrollable giggling. However if you like things that can survive a few hits, then I suggest you leave it in the store, despite what the salesman with the massive smile says.