It depends if you are talking about a jib cunningham, or an adjustable forestay.
A jib cunningham allows you to adjust the tension in the luff of the jib.
An adjustable forestay allows you to adjust the tension of the rig, via the tension of the forestay.
We had a jib cunningham on 2694, but only because of the zip luff, and it was the easiest way to terminate the halyard. I can't say we ever adjusted it on the water, it just occasionally let go on us (which was very annoying). That was just a cleat under the foredeck with a line lead back to it to adjust the tension. Not very fancy. We did used to adjust the tension of the jib depending on the wind strength for the day, but I can't say it's something i'd necessarily bother with again.
An adjustable forestay requires quite a lot more hardware, as you will need a purchase system capable of pulling on your rig tension, (think boat breaker... but attached to your boat) which is then lead back into the cockpit. This is normally in addition to adjustable shrouds, so that you can adjust your rake and tension on the fly. This is very I14 thing and I am sure it is very fast if you know what you are doing. Probably not any faster than setting up your boat and sailing well without the additional weight you will add though.