Welcome to ECF, I use nicotine river pretty exclusively, and I like them. I don't know how their prices compare to other vendors but I like their
nicotine salts and the fact that I can
buy flavors from many different vendors including their own proprietary flavoring. I find them to be quick, reliable and easy to work with. My products arrived clean, neatly labelled, etc. I think you will enjoy your mixes.
Steeping time does decrease with an ultrasonic flavor for some flavors. Some are pretty much shake and vape, and don't need steeping. I'd say it's going to vary a bit with your flavors, some just seem to not do well with an ultrasonic bath, some flavors can get muted. I'd say try your flavors in 3 days and see how they are doing, it will also depend on type of flavoring, custards and creams seem to need more steeping time. You will have reduced the time fairly significantly, though, most likely.
I like to steep by waiting and shaking, to me that's the most reliable method for all my flavors, but now that I have DIY going, I can mix up batches ahead of time and just steep. It works out well.
Anna