Yes, it's different from what other member talking about. While it's open source, this is first time i heard this wallet and looks like it's not popular (total star only 51 & 7 on GitHub).
As I understood, an private key starting with 5, give a legacy address only, and also give an uncompressed adress.
Yes. Uncompressed WIF keys start with 5 and should only generate uncompressed legacy addresses. You can use them to generate other addresses, but these address will be non-standard and it will be very difficult to successfully spend any coins sent to such addresses.
And here's example how
difficult it is,
https://bitcointalk.org/index.php?topic=5192454.0.