I don’t see any problem using Sefaria. The first seforim ever printed was printed by non-jews. I also don’t see the comparison between Sefaria and Hebrew books. Hebrew books are specific seforim which are scanned. If you have to find a certain passage in a sefer Hebrew books is good, but you often have to scroll through many pages until you find the page you are looking for. Sefaria on the hand is unformatted but its major accomplishment is its cross-references You can scroll any posuk or gemara and find not only meforshim connected to that posuk, but any place that posuk or gemara is mentioned in many seforim.
When I was learning In Torah Vodaath I asked Harav Belsky Zatz”l about using Jastrow, he told me “if you had a Greek word you don’t understand you could ask a greek person. You can use Jastrow.”
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