There is no free lunch in investing, so that extra yield comes with extra risk. Be that duration, credit, etc. That's not to say MBS's don't have their place, but I would never claim people's mortgages as equivalent to cash in any shape or form. Your website claims MBSF is safe for 3+ month durations, but that is not the avg duration of MBSF held securities, so you are encouraging duration risk.
I haven't read the full prospectus on MBSF, so I'm not an expert on that product, but it seems expensive and complicated, which is not what you want for cash and cash-like things. This should be a hard pass for literally everyone.
Meanwhile you can hold something like ICSH[0] or SGOV[1] with expense in the .09% or lower range(i.e. for every $10k we are talking $9/yr or less in fees). SGOV is 0-3 month max duration, so it's perfect for holdings in the 3 month time-frame. If you need longer time frames you can buy govt bond ladders in whatever time frame you want.
What your product should have been: You specify duration for each of your buckets, and then you pick appropriate, cheap index-based investments that are cheap and easy to reason about for each of the buckets.
0: https://www.ishares.com/us/products/258806/ishares-liquidity... 1: https://www.ishares.com/us/products/314116/ishares-0-3-month...