Amazon Echo has been extremely unreliable with unsupported integrations (i.e: blinds, Harmony, garage doors, etc). For this reason, your best bet is to use IFTTT and use “Trigger Open Blinds” along with virtual switches. What works today, might not work tomorrow with native Echo commands for unsupported device. You can continue to use On/Off as that seems to be reliable.
https://community.smartthings.com/t/echo-naming-quirks/21080