I've had Gumi for several years and no problems with winter damage, zone 5b.
Pretty red berries, sweet sour taste. In my opinion the taste very much like autumn olive, Eleagnus umbellata.
Nice crop this year and a waited about 2 days too long to pick them. Birds got the entire crop. Was going to juice them.
Three years ago while traveling in Thailand I found Eleagnus latifolia fruit in a fruit market. Looked like E. umbellata and tasted very much the same. Size: About the size of my thumb. Now if we could just make a hybrid.