Remember that ALL rack mounted electronic gear produces HEAT.

Heat is destructive and dangerous to computerized stuff, (anything digital) and is an absolute killer for amplifiers. If you plan to get the cheapest smallest bag to house a digital effects unit, a preamp, and (especially) an amplifier, you are far better off getting more spaces than your equipment fills. I suggest AT LEAST double the capacity for even marginally adequate ventilation.

Don't forget that this type of rack bag is PADDED. Padding means “insulated.” When it comes to keeping your gear cool, happy and functional, insulation is the OPPOSITE of what you want. With standard plastic or even hardwood cases, which you can still easily carry or roll, you can install a forced-air cooling fan in the rear. I have yet to see that done for any rack bag.

Can you simply remove the equipment from the bag before each use, set it up, plug in the power, plug in the audio cables etc. then reverse that process for tear down? Sure… That defeats the whole point of having rack gear in the first place: Convenience.

If you are carrying only one cherished effect unit that is not an amplifier and not digital, (in other words, some device that does not produce nor is affected by heat) then sure, a one or two rack space bag is cool.

I’m just trying to think of what any musician might carry in a rack bag that isn’t digital, or an amplifier of some kind (pre-amps included) or that does not produce heat.

…Just some things to think about so you can make a wise decision.