I typically don't mess around with Umbra until my character has a decent chance of standing their ground with her. I prefer to engage her in honorable battle; not spray her from head to toe with aerosol cheese.
I'm also not interested in premature possession of the Umbra sword. At low levels, with sneak bonuses, it's just too ridiculous.
Same as Honorblade, zero weight end game quality weapons, because they are essential, you cannot be disarmed, and if you hotkey them, you can keep them in jail.
Sounds good, but eventually you will find that all the fun and sense of achievement is gone when you find other weapons. The first time you find a marauder warlord with a Dwarven longsword, the first time you kill a vampire patriarch, and get an elven shortsword, all wonderful moments, unless you get Umbra or the Honorblade too early, then anything else is relegated to the 'loot to sell' category.