What you require, really depends on the application and test envioronment.
What are you planning to Bode plot ?
Things such as frequency range, noise floor and dynamic range are pretty obvious, and many measuring instruments these days have some excellent features. If you are studying just analog type circuits, amplifiers, filters, servo systems etc... that is all pretty straightforward.
These days switching power supplies are a significant area of interest, and Bode plots are just about a must have, if you wish to maintain your sanity.
Switching supplies are are very Bode plotter unfriendly by being significant producers of wideband noise by the power components.
Trying to resolve a sine wave of a couple of millivolts submerged in hundreds of millivolts of spikes and ripple is something very simple equipment is just not capable of doing. Its all very well the software being able to plot a nice smooth gain curve over 100db dynamic range, but unless millivolt or microvolt level signals can be resolved beneath huge levels of noise, the pretty plot on the screen is just not going to happen.
Many if not all low end Bode plot systems just use direct analog to digital conversion and some clever number crunching. That works fine for demo purposes by the plotter salesman, but not when trying to make real world measurements on switching power supplies or in really noisy applications.
The only way to do it is with a couple of very narrow band swept filters, similar in concept to a spectrum analyser. That can be done either with hardware or very sophisticated software to reject everything but the exact test frequency being run through the equipment under test.
All very clever, but it does not come cheap unfortunately.
So a simple low end Bode plotter may be all you need, or it may not work for you at all, depending on the test environment.