For good "controlled unpredictability"? I have the following recs:
Wogglebug. Very popular, but I still think that most people under-utilize it. It can be manually clocked up to audio rates, so you can use it as a "bitcrushing" effect (actually sample rate reduction, so bitcrushing is a misnomer... however, that's what most people call it). Regardless, it can generate on its own or take any signal and hold it with slew and bounce. You can mix between the internal noise source and external input. There's a lot here beyond pure random.
SSF Ultra Random Analog: I don't own this, but it's a similar design with a bit more open of a circuit. Like Wogglebug, if the internal noise source is too unpredictable, you can patch in your own source to derive random from.
Just Friends: Not a random source by any means, but to me this is one of my favorites for unexpected modulations. I like to set up traditional patches and then manipulate the Intone control to send the modulations out of sync with each other.
Ornaments + Crimes: Such a killer module. I have two of these, as every "app" on here is useful. There's a quad quantizer on here. Each quantizer can be manipulated independently or together. Each quantizer can receive a separate input or use a built-in random source (LFSR like the Turing Machine, Logistic Chaos map, and more). This playlist is fantastic: https://www.youtube.com/playlist?list=PLxzWZ5Bv5AwyYk5KDnGvEHWs8CzAXnvec The Temps Utile is the gate and trigger counterpart.
Teletype: This works really well on its own (you don't need any other Monome devices). The built-in scenes are perfect starting points for controlled complexity. Most of my patches use this or O+C as a starting point.
Sport Modulator: If you're interested in the Smooth/Stepped Serge, this is basically that. However, in cycle mode it produces a bipolar signal. The advantage is that either side can be switched to operate in Smooth or Stepped modes, making it ultimately more versatile and much more space efficient. The R*S SSG is a lot easier to learn, though. For a brief period, I was using the SSG a lot more to train myself, but I sold it and returned to the Sport Mod. Watch the last few patches in this video: https://www.youtube.com/watch?v=oeuxMe_hpcM Really, combining this with Maths gives you practically identical functionality to the SSG and DUSG. I should add that Maths, Sport Mod, SSG, and DUSG are not inherently unpredictable modules. The unpredictability comes from clever patches like the ones in James Cigler's video.
Plog: One of the most underappreciated modules in Euro. Not random at all. It has two six-mode logic blocks that can be used as 2-in or 3-in, along with two flip-flops. The normalization scheme is just solid design: the first logic block's inputs cascade into the second. The output of the second is normalled to the first flip-flop, the output of which is normalled to the second. By using two gate inputs and modulating the logic modes, you will get into highly unpredictable territory all derived from those gates. Here's a good demo on that: https://youtu.be/NvrxQbh6vAg?t=1406 (skip to 23:25)