I've had a couple of different types of e-bikes, starting with one to keep me going when I was recovering from hip replacement. I have one that's in the BST now, coz now that im fully recovered I ride a manually-powered bike for exercise. You can read about the e-bike here:
https://www.carolinafirearmsforum.com/index.php?threads/electric-cargo-bike.143950/
Like most things, what you want depends on how you're gonna use it. The store-bought bikes have gotten much better over the last few years, but the low end hub motor bikes are kind of gutless. OK for moderate easy rides on level ground. I wanted one that I could be more comfortable mixing it with traffic and hills, and that means a mid-drive, driving through the bike's gear train. I also wanted some real range, and that means a big battery. I think you could weld steel with mine. You need to have a healthy respect for the batteries, if they are damaged or improperly charged, they can make a real serious fire. I only charge mine when I am able to be in or around the garage while it's on the charger.
If you care about more than just a little tailwind while riding, be prepared to spend some money. What
@Timfoilhat says about weight is true too – I'm guessing mine weighs about 65 lbs. I can hoist it into the back of a pickup but it takes some loud grunting.
Luna Cycle, who built mine, offers semi-custom high-performance bikes and kits. I've been very pleased with mine, and if I was going to buy something like this again, I would certainly look at them. They do assume the user will have a reasonable level of experience with bicycles and stuff.
https://lunacycle.com/ PM me if you think you might want the one I have in the BST; I'll make you a deal and will figure out how to ship it.