HERMS is a bit cleaner and easier for me, and I take personal pride in hitting my numbers exactly over and over. BIAB tends to be a bit more variable with grain and efficiency with the no sparge. You have to calculate your water and grain exactly. As your mash gets bigger, your efficiency will go down, so it was somewhat frustrating process for me at first.
BIAB, like batch sparging, is a much more consistent way to hit numbers, both volume and gravity, than fly sparging. I think a big part of why people are not experiencing these benefits is that no brewing software correctly accommodates BIAB, or batch sparging either, for that matter. BIAB and batch sparging need to based on conversion efficiency in the mash, then worked forward from there based on transfer losses and grain absorption.
There is a work around that isn't too onerous, and it can be used with almost any brewing software. The solution is a spreadsheet from some Aussies called CE-BIABcalc that will give you a new grain bill based on a grain bill for a non-BIAB recipe. It will also give you new eff numbers, water volumes, etc. Another advance, besides CE based calcs, is the water absorption method the guy (Stux) used- 'true absorption'. It is the most exact method. I have been hitting my numbers dead on, regardless of different gravities or volumes (for different trub levels for pellet vs. cone). This is usually for first time, or converted/scaled imported recipes. Of course the numbers I am hitting are just grav and vol, because eff changes with each grain bill, but I hit the eff number it predicts by default when I hit the others.
The spreadsheet will also handle batch sparging, or a BIAB 'dunk sparge'. With these, effeciency can be upped to within 5% or so of fly, or for normal grav beer even match it using a fine grind (but the flour can be an issue). If a software package were to incorporate the spreadsheet equations, it would simplify things greatly for BIAB and batch spargers.
I doubt fly sparging could ever be as predictable as batch or BIAB using the proper calcs, at least not based on my experience with both. Maybe if the fly sparge efficiency were low-balled and the sparged stopped early, but then its only advantage kind of disappears.
Another reason for efficiency unpredictability in general, is that some packages, namely BeerSmith, uses a bastardized efficiency metric. BS's "Brewhouse Efficiency" is calculated as 'to the fermenter'. This is wrong to start with, but is compounded if any changes are made to trub loss. If you adjust trub values in BS, and don't adjust your Brewhouse Eff, it will give you bad numbers. Tip: set trub/chiller loss to 0, and keep a note of trub losses elsewhere (like in the fermenter losses field, since nobody uses that anyway).
Also BIAB involves pulling the bag and draining over a grate in the pot, messy splashes, and very hot on your hands when you pull that bag out of 170 degree water. Now that I have a 3rd pump and transfer the wort in the way that I do, all I will have to do is drain the BIAB wort into another vessel and that will eliminate pulling the bag from my process. So in short, I think BIAB will be a lot easier now, albeit not pure BIAB, it is a no sparge process with two vessels really. I will still use a bag for my grains so cleanup will be easy, but I won't have to pull it from a hot mash anymore.
This grain bag lifting is an issue with BIAB in its pure form, hence all the contraptions for hoisting. You think 7g batches are tough, try 18gal/50lb grain bills without any hoists or help, or even a basket, and also while standing on a chair. I will be changing that soon, hopefully. There are a lot of guys doing MIAB using a gravity drain into the kettle. The bag is just used as a filter/false bottom or to help with grain clean up. Some do it to get a little more efficiency using a fine grind.
