I suggested Tripp-Lite specifically as it generates "Hospital Grade" conditioned voltage, and does not use a ferroresonant transformer. Agreed that ferroresonant transformers are quite dirty and cause all sorts of noise downline if not very carefully managed. http://www.tripplite.com/2400w-120v-power-conditioner-automatic-voltage-regulation-avr-ac-surge-protection-6-outlets~LC2400/
For specifications - note the EM & RF filtering, not typical of the cheaper models.
This unit also meets ANSI Standard C84.1-1995 (R2005): http://docslide.us/documents/ansi-c841-1995-r2005.html Which, essentially, is the standard that power companies are also required to meet.
Now, the issue with variacs. They are fixed devices inasmuch as varying input means varying output. Which means constant fiddling if you are in a typical residential situation where voltage may vary from as low as 108V during the heat of the day - not quite a full brownout, but not 120V either - to as high as what I measured once of 131V at our summer house. That is a 23V variance, admittedly in two different locations, but both where good audio equipment is in regular use, including considerable stuff from Dynaco.
So, my preference is to use a device that manages a constant, filtered voltage, also with surge protection at a reasonable cost and with neither objectionable noise (audible), high cost or taking up too much real estate. I run equipment from Revox, Harman-Kardon (Citation), Scott, Dynaco, AR and more through my LC, without any discernible noise or distortion resulting.
De gustibus et coloribus non est dispustandum.
One more thing: Variable Auto-Transformers make heat. Accordingly, the rating of the Variac *must* be at least twice the anticipated load if the unit is to be left in place at all times. These devices were designed to dim lights, not manage wonky power. Just keep that in mind when using them "Off Label".
Lastly: Analog vs. digital meters: This is very much a matter of taste, assuming that both meters are both accurate and properly calibrated. An analog meter shows 'dither' better than a digital meter - the needle bounce is far more noticeable than a shifting last digit, and the timing of the variance is much more easily discerned. Where I am watching for those variances, a mirrored analog meter is my preference. When I am measuring to/for a specific volt/amp/capacitance/resonance/whatever, I do very much prefer a digital meter.