A lot of people really like the Rytm. Personally, I do not- so I can’t recommend it(I didn’t find the synth parameters to be as vast as some of the other machines Elektron offered.
For actual techno, it’ll probably suit your needs.
The Octatrack can definitely work as a drum machine. It can (mostly) work however you want it to. For drum machine purposes, just load up your samples and plug away. You can even sample lock per step so you can group hi hats and snare on the same track. Once you lock in your pattern, then you can take your percussion to the moon and back.
Disclaimer- if you want a decent variety of kits that you can pull up and work with on a whim, then you’re going to want to get something like the Rytm/A4/Machinedrum as it has the traditional kit structure. If you want a wild and chaotic variety of sounds, you’re going to want the Digitone/Digitakt as every new pattern will be a fresh canvas to work with. There’s sorta a compromise with both on the Octatrack as each bank of 16 patterns you’ll only have four kits(“parts” is the official terminology) and while you have a more static kit structure you’re more able to dynamically alter the sounds coming out of the pattern live(though an argument can be made for the Rytm having more performance abilities- I’m going to just say it’s different, the OT just seems to have more room for variability- personally speaking)
Performance speaking- the Digis are quick performances macros(control all) that don’t require as much forethought as the other machines listed- easier to warp everything on a whim but you have less control over the madness you’re inflicting on your sounds. The other machines have legitimate macros, but it can be difficult to incorporate programming those in as part of your workflow)