The biggest benefit to Manna is that the wait time for a table is considerably shorter than Gen. Aside from that, I think Gen is still the superior option, with a tastier selection of meat and sauces.
The service was good. The atmosphere was less trendy than Gen, but that wasn't a drawback for me (I tend to like quieter places better anyhow). What was nice was how big the serving sizes were - they definitely don't skimp!
You don't get seated until the entire party is present.
However, I prefer Gen for one reason.
The reality of it all is that Gen offers spicy fried Korean chicken wings on their basic menu, and Manna BBQ does not.
And I really, really like having fried chicken as an option for KBBQ.
Take a look at Manna's basic non-premium menu. If the selection looks good enough for you, then it's probably more worth it for you to skip Gen's super long lines and just go here.