You’re actually in a really good spot because you’ve already test ridden a few - that’s what usually gets people from “idea” to actually using one.

If a bike felt safe, comfortable, and natural like you said about the Segway, that matters more than almost anything else. Fit is what determines whether it becomes something you ride all the time or something that sits.

On the “will I actually use it” question, most people who stick with it treat it like a replacement for short car trips, not something they “should” do for exercise. Your 3–6 mile errands are pretty much perfect for an e-bike, that’s where they really shine.

On theft, the advice you got is pretty solid. Taking the battery out doesn’t really stop someone from stealing the bike, it just prevents the battery from getting stolen. What helps more is making your bike the harder target with a good U-lock, ideally a second lock or cable, and just making it look like more effort than the one next to it. Being on an upper level patio definitely helps, I’d still lock it though.

For your knee, what you noticed is important. That “feet behind you” feeling usually comes from the bike’s geometry. You’ll likely be more comfortable on a step-through with a slightly forward riding position, not super upright like a cruiser but not aggressive either. Aventon and Velotric tend to hit that middle ground well. Electra can be very comfortable but the pedal-forward style isn’t for everyone. Pedego is very comfort-focused but usually more expensive. The fact that the Segway felt right is a big signal though, I wouldn’t ignore that.

On brands, I’d think of it like this. Aventon, Velotric, Trek, Specialized, and Cannondale are generally safe bets. Lectric, Ride1Up, and Segway are solid budget-friendly options. I’d be more cautious with random no-name brands because parts and support can be an issue later. I wouldn’t worry too much about the “Rad is dead” comment, that’s a bit exaggerated, the bigger thing is just making sure parts and support are available.

For new vs used, used can be a great deal but the battery is the biggest unknown. If you’re new and don’t want to deal with diagnosing issues, new is less stressful. If you go used, try to stick with something 1–2 years old and test the range if you can. One thing that was good advice in the replies is that some shops won’t work on bikes they didn’t sell, so it’s worth checking local shops first.

A couple things people don’t always think about are the weight of the bike, which matters a lot for apartment living, how easy it is to bring inside if needed, and making sure it has a rack or can take one if you plan to carry stuff. Also worth looking for a UL-listed battery for peace of mind in an apartment.

Honestly though, based on what you said, you’re already narrowing it down the right way. If a bike felt safe and comfortable and you can picture yourself actually using it for those short trips, that’s usually the one people end up happiest with.