Talk to me about folding bikes

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My wife is going to have to take the commuter rail into Boston three days a week next year (beginning in the Fall). Therefore, she is thinking about getting a folding bike so she can take it with her on the train during peak hours.

The ride from our house to the train station is ~ 5 miles. She will then need to ride it from the station downtown to the university where she works which is ~ 3 miles.

What are some the down-sides of folding bikes?
Are there any specific brands beside Brompton we should look at?
Any specific brands we should avoid?
Anyone have experience commuting on a folding e-bike? She isn't sure if she wants an e-bike but just curious what other people have experienced.

Thanks!