Hi El Chiguete. I'm not that familiar with newer harmonisers but it probably compares quite well even though it's quite an old unit. I bought it many years ago (~25 or so). Its never missed a beat over thousands of gigs so very reliable. Back then it was the bees knees and affordable. Other units of the day were very expensive. I think I paid around $500 AUD back then so it wasn't cheap even though I got it on sale. It's main claim to fame was being a smart shift i.e. you tell it what key/scale you want and it adjust the various harmonies (intervals) to match the key/scale. So I set up some banks with harmonies in various keys (E, A, B, G, F# etc) to suit the set list. It gives you 2 separate selectable/programable harmonies per patch (2 above, 1 above 1 below, 2 below) and can also do a very nice chorus (without modulation). It's mono in (guitar/line selectable) and you get the 2 outs. It also has a distortion loop on the input so you can plug the guitar directly into the input and put a distortion device (in my case MP1 in the early days and now MP2) in the loop. This was to assist in tracking the note as harmonisers can struggle to get the right pitch from distorted guitar. I ran it like that initially (with MP1 in its loop) the return feed from the 3rd effects send of the little mixer I use (see post on how do you connect your rack gear). All I/O is on the back of the unit so it was a bit of a pain to have to plug the guitar in from the back so I stopped using the loop and it still tracks fine. I found the interface easy to use and well laid out. It only has 99 patch locations so these days I set it on a octave up and down and use ADA patches above 100 so it ignores midi changes and I use a bypass switch to include it when playing. My unit has a little physical hum as the transformer vibrates the top cover, if I take the cover off it stops, a bit annoying but you can't hear it when playing. It also has a tuner function, not bad but not as good a peterson strobe tuner but better than Roland tuners which have quite wide dead zones. Digitech made a foot switch for it but I've not used one.
So in summary, very reliable, programable for lots of different scales/keys (including augmented and diminished), 2 harmonies, tracks well even playing fast and has the distortion loop if your sound is too distorted for it to track reliably.
You can hear it (https://www.youtube.com/watch?v=sIr9nZ4aJfo), I play the 3rd guitar solo. I think I had it set to a minor 3rd in G (one of the patches I ran up for highway star). This was live in a warehouse and my original MP1.
Cheers Richard