This project is mostly intended to protect from "software" (trojans, etc.) extraction of ssh key and to provide more reliable method of storing keys than just keeping them on disk storage. It might not be as protected as smartcard against all physical attacks, however in some cases, it is more protected as it's transparent and wont have hidden backdoors like smartcards (e.g., CVE-2017-15361) and uses very simple protocol to reduce probability of software exploits using "corner cases" of protocol, such as, for example ASN.1 prone to have overflows and leaks (MITKRB5-SA-2009-002, MS04-007, CAN-2003-0545 and much more), due implementation complexity. The most important feature is the smallest possible size of the firmware. This will allow you to have a hardware dongle that can keep 3+ RSA4096(DER encoding) on 64k flash, or whopping 30 keys in 128k flash. As alternative you can take a look to gnuk, but it generates 110592 bytes firmware (current git snapshot), while Blue Pill have only 64k flash (officially).