You get what you pay for -
and VX-I is the cheapest in the VX series. Only the Rifleman, in the Leopold line, is cheaper - by only about $20 , I believe.
So, you can expect The VX-I to have fewer lens coatings, which are expensive to add, and therefore the dimmest, least defined, least color correct image. This means early light of morning and fading light of evening it will be a dark, fuzzy, indistinct image, where you can't count the points on a buck's rack, or even separate the outline of a deer's back from the weeds/brush in front of him, or the trees/brush behind him.
If you are just intending to "punch paper" at the range during good light conditions, you could probably get by with a VX-I, but don't take it hunting! IMHO. Take a VX-II hunting, or the new VX-3 (especially designed for early and late dim light conditions).