You don't install anything on your Wii U. You use a web browser exploit. So effectively yes, it's like hackless Project M.
http://loadiine.ovh/gate.php
Basically to load things like Homebrew Launcher (for various things, but in this case, you need it to dump your game), and SDCafiine (the thing used for loading Smash mods from your SD card), you need to go to the above URL from your Wii U Web Browser (just Google "loadiine" from your Wii U Web Browser and it's the third result. Make sure to bookmark it too if you're gonna play Smash mods regularly).
This website allows you to boot up these programs without actually installing them permanently on your Wii U. Homebrew Launcher is something you only need to use once for Smash modding. Every other time you're just using SDCafiine (which is essentially a program that takes you less than a minute to be finished with each time).
Be aware though, dumping your game will take like, half a day, if not nearly a whole day. So you're best starting this process early in the morning, or if you're willing to leave your systems on overnight then that's another option. Alternatively, you COULD just download a game dump from the internet if you don't want to bother going through Homebrew Launcher, but since distribution of those is illegal, I'm not linking to anything here so you'll have to sort that out on your own if you go this route (I admittedly took this route myself, though this was because I misunderstood what dumping your game would entail - I thought I'd need to buy a Blu-Ray disc reader, when it turns out you do it using your internet connection. Really bizarre to me, but it works). There are also risks with this route, like going to a fishy site and downloading the dump from there.
Once you dump the game, there is a program you can download to your PC called Uwizard, and you will have to use this to download a dump of the latest update data for Smash Wii U. You need this to play your mods on the latest version, and to be able to mod DLC content.
Once you've got those two steps out of the way, you are pretty much done with the initial set up, and that's the hard stuff out of the way. After that, you're just setting up Smash Explorer (this program allows you to explore the dumped files, and you can drag your mods into the correct folders to mod the game - this is why you need to get a dump of the game and the update data), and downloading/making your mods and putting them in. Smash Explorer then allows you to create a "mod package", and you do that. Then it will prompt you to copy it to your SD card (which also needs certain folders set up in advance, which you can see in the video). It's at this point you put your SD card in the Wii U, and load up that URL I linked to. After that, select SDCafiine, boot it up, do what needs to be done there, and then launch your game, mods and all. You need to boot up SDCafiine every time you want to play with mods, which is handy, as it means you can still play the vanilla game with ease.
If you have any questions or want me to walk you through it, then PM me, but I can only go over so much in public for legal reasons.