Comparing the Tactical Grapple Gun (Hard Targets, p.187) with the standard Grapple Gun (SR5, p.449). The standard grapple gun has "an internal winch that can pull back the grapple (or pull up small loads)." The tactical grapple gun specifically calls out an "upgraded winch motor," without saying exactly how it's been upgraded. It seems reasonable that it would offer a bonus to the Climbing Test, at least for lighter characters.
Strictly off the cuff, I'd say smaller PCs up to 100kg (see Metahuman Characteristics Table, SR5, p.380) get double the usual +2 for assisted climbing (see Climbing, SR5, p.134), or +4 total, and ignore penalties for difficult climbing surfaces. This ought to get even unskilled climbers up most walls. Heavier PCs (100-200kg, mainly orks) get only a +1 bonus (+3 total) as the winch struggles to counter their weight. PCs over 200kg (i.e., trolls) would get nothing beyond the standard +2 for assisted climbing. The winch flashes an error message in AR, and offers directory assistance for renting a construction crane.