I had experience with the early G system- we "needed" to use favored analog effects pedals in the loops- the G system did not have the headroom to accept our typical gain pedals cleanly- the guitar used had some of the electronics of the Clapton Strat and the g system couldn't handle the wide dynamic range.
In the end it went from the band's lead guitarist to the supporting guitarist who had a narrower range of needs. Even so we absolutely needed to use some other pedals- ..and life has changed since then
With current guitarist, very exacting and demanding- we started with the HXFX and had some very impressive result right off with a variety of the effects, we notice ( as yet) no latency through the a/d converters.
We have just purchased a helix and will continue to explore the technology using ONLY the effects as we have amps we are very happy with ( and although using line6 and other modellers since the 90's..if you have a Hiwatt or a tweed or a trainwreck, well just use the real thing).
the first thing you will gain is the increase is processing power, converters, bitrate- etc, and the experience of millions of users over many many years, to detail which features are truly useful.
we don;t know if the helix will replace the effects in a switching system with 30 loops- but it's a lot lighter!
some of the effects we like have character with we think we will need to retain and use with helix- a boomerrang V1 not only has sound, but the operation is quick/easy- also the Whammy V2 has a charm to the imprecise sound- as does the old ibanez dm2000 with the mod and hold functions.
if unsure and are amazon prime member, get one there- returns are easy
cheers