I believe ALL boats need to have a viable way to get back onboard. whether or not the water is warm enough that you will ever purposley swim from the boat or not, the colder the water, the more necessary will be the need to get out of it in a hurry if a situation develops....and if you do commonly swim from the boat, the more necessary is the need for a stout, easy to use ladder...
I have a ladder similar to the folding ladder shown, on our 25, and had the same on our 21... I like it and think its the best way to go, short of having a boat large enough to have a fixed ladder. its very solid even with my 210lb frame on it in rough windy conditions.... (the ladder is long enough that in warm weather and waters, some of the crew will sometimes take a dip on the ladder while underway to cool down)..
personally, I would not waste my time with the telescopic ladder, as I have had too much experience with them on power boats, where in some cases they can be a more aesthetic installation on a sleek boat... some sailboats are sleek, but ive never seen one sleek enough that a folding ladder on the stern ruins its looks... a folding ladder is more rigid and so it is, or can be longer, it never sticks or jams as it gets older, very seldom holds water, is quickly and easily folded/stowed, and ive never heard one have a vibration rattle.... this is not true of all the telescopic ladders Ive seen... and a folding ladder can be modified if desired...
the one shown below on our 25 reaches well into the water. it is mounted on hinge brackets (which seems to be the most common mounting method for swim ladders) so the upper part can also be folded away from the hull so its easier to wash under it.... a simple bungie loop with a plastic hook permanently looped around the taffrail stanchion (not shown) holds the ladder firmly in is stowed position,
the transom of the boat has an angle, and so I didnt like to crawl up a ladder with an inverted angle, so I extended the standoff legs, which is simple and can be quickly done in a couple different ways.... then I wanted the folded ladder to fold in closer to the boat without tipping the upper hinges which would kick the stand-off legs away from the hull, so I removed the lower hinged section and tweeked it a bit so that when installed it stowed as I wanted it... and with this modification, it also allows the lower rungs of the ladder to rake rearward a bit more, and so its easy to stand on the lower rungs without feeling like your hanging upside down on the boarding ladder... all this can not be done with a ladder with only semi rigid joints in it.