Foreword: These are strictly opinions of fellow Fortress: Destroyer players. Do not solely rely on everything on this page, as it may be biased. Instead check the page of the tower itself as all information there is straight fact.
The hardest hitting cannon in the game. This tower is very powerful, especially for bossing, but the inability to hit air units limits its general purpose value. Use is recommended if you already have several other towers that can hit air units, and if it has decent tier and slots.
The best small cannon you can get. Good damage and not bad ROF with the downside of it can't hit air like most cannons. Put a Shock Spike module on it.
An absolute pile of junk. One of the worst cannons in the game.
I have a negative impression of this tower as well. For six cannons in one you would think it would be quite powerful, but its not. The ROF is just too slow for it to do much.
By far, the best Medium Cannon in the game. High DPM with air targeting puts this tower above most autocannons. Very much worth using if it has decent tier and multiple slots.
I discovered what is, IMHO, the ultimate weapon. If you combine the Buckshot 12 with the Shock Spike module, or better yet, two, and also with a Shrapnel module, Explosive Shot is best, you have a weapon that can easily clear up to 12 units or several areas of plasticyte in a single shot. The secret is the combination of the shrapnel and the 12 rounds launched at once. The electricity travels along all paths, my observation. You can wipe out whole areas of enemy units in a single shot. Yes, the rate of fire is slow, but with two high tier Shock Spikes you have about a 90% chance of a critical hit. Try it and see. Let me know if it works for you. (I play on the iPhone 7.)
I feel like this thing is totally underpowered. I mean 12 20mm barrels? This thing should be a monster Gatling Gun!! ...but it isn't. It's a cannon, and a crappy one at that. Yes, 12 shots can pretty much kill anything, but it has a slow RoF, and the short range doesn't help. If they made this a Gatling Gun, I'd use it in a heartbeat, but as a cannon, no way.
If it was a gatling gun, that would be way to overpowered. I use it on one of my Infiltrator corvettes, but not as a main gun. The Harpoon missile launcher has that duty.
This tower is far from the best for the reasons stated above, however I would like to share a few positive features. First, the Buckshot 12 can target air which is quite rare for a cannon so this is a good option if you don't want to sacrifice AA power but need a cannon (for adding something like a Shock Spike to). Second, it has a built in crit chance, and especially if you raise that with a crit chance raising module with all 12 shots you'll be getting critical hits left & right. Then add any module that activates on a crit.
The Atomic Spokesperson, 20/4/2016
The Horizon is a great medium cannon of rare rarity that can be accuired at the start of the game. It is a great cannon with high output damage and medium fire rate. It is a great competitor to the superior Vanisher, and a great replacement for quite a few other medium cannons.
I actually got this one rather late in the game, even considering that it's Hyper-Rare. Despite the fact that it can only hit ground and air (like most cannons :L), it's still pretty good for its DPM and Pellet Damage, although its ROF is crap.