A lot of what we want to power with electricity is just converting it to mechanical energy. What if the pedal powered a flywheel, and then gears engage the flywheel to power the device?

Seems like a fair bit has changed in 15 years, batteries (Lead Acid, really?), inverters, even generators are way more efficient. At the end of the day it's only 100-150W in, but even at 50% chain efficiency, 100W for 1h = 50Wh = 10000mAh = ~ 2 phone charges, which is not nothing.

The flywheel (replacing bike and rider inertia) for greater biomechanical efficiency is a well taken point and would lead to a more consistent power output.

Rebuilding it as a general purpose rotating spindle which could attach to a generator, a blender, a multi function food processor, grinder, sewing machine etc. could go a long way towards making a useful device.

From 2011. Their solution to compress air is poor, unless air powered tools is the energy user. Still pedal powered generators have not improved much. Rollers is best because of gearing, but it requires a bike. With a bike that is cheapest/simplest device, but requires room, and possibly moving bike indoors.

This is why that Rivian bike is so very stupid

It is nothing compared to the energy used to produce the setup.

Sure, if you use energy to produce it new instead of repurposing (as said, rebuilding) and can't amortize over a long timeframe. Reduce, Reuse, Recycle. If you take things destined for landfill and adapt them it's fine, likely a net win, with a good fitness boost. It's the design that would be important.

Also while the power output is not huge, human muscles are capable of some impressive torque, especially with geared mechanical advantage.

It is nothing compared to the energy used to produce the setup.

What is missing here is the fuel input - the food humans need to consume to power such a device. Everybody here knows how many calories riding a bicycle hard can burn and those calories need to come from somewhere. Growing plants to feed them to animals which are then slaughtered and fed to a human who is processing the meat into energy which is going into such a generator is really, really inefficient. Getting those calories from plants is better, but a solar panel with a battery is better. Simply taking the energy from a grid which is powered from renewables might be even better.