Ben - i came to the same conclusion as you from Jonker's website. If I have understood well from Andy Davis (UK distributor) then the JS-1C is one model with three tip options: 18m, 18m Evo and 21m. The inboard wing section, and indeed everything else apart from the tips is the same regardless of which tips you choose. If you buy a JS-1C 18 Evo then you are buying a JS-1C with 18m Evo tips rather than the standard 18m tips.

On Friday, May 15, 2015 at 9:28:20 PM UTC+1, wrote:
OG, thank you for your JS-1 feedback. Respectful congratulations; your accomplishments in the JS-1 21m are nothing less than world class outstanding..

You are one of the few people in the world who has the experience to answer these questions. I'm assuming the JS-1 C 18/21 model uses the 18m EVO tips when in 18m span. Since the center section of the JS-1 C 18/21 has to be stronger (meaning stiffer) to handle more wingspan load, how much more does it weigh than the center section of the JS-1C 18m EVO? When in the air, is there a noticeable difference in energy "feedback" between the JS-1 C 18 EVO and the JS-1 C 21 with 18m EVO tips? In your opinion, does the JS-1 21 flying the 18m EVO tips give up any performance to the "pure" JS-1 18m EVO?

Thank you for your responses.

On Friday, May 15, 2015 at 3:34:44 PM UTC-4, OG wrote:
I've read the posts with interest, and some valid and some invalid points have been made. Looking at performance, the 29 is is really good, and had the edge on both the V2 and the old JS, especially so in good weather, when running hard. The 29 handles really well, but the 18m JS handles better, and gives more input to the pilot on where the energy is, especially at mauw. The V2 climbs well, but cannot run with either the 18m JS or the 29. Rigging the 29 is easier, as the JS inner wing is heavy, but if you have a hangar or rigging aid this is a moot point. Very little to choose between the JS and the 29' although I believe the finish on the later JS's are slightly better than the 29, and the 29's wings warp after the 2nd season. Also, the new evo has the edge on the 29, judging by the runs we had at the Grand Prix in Worcester.
The best production open class glider currently is the EB 29, but there is really very, very little difference between the two (almost like the ASW 17 was just a fraction better than the Nimbus 2). But at three times the price of the 21m JS, and an animal on the ground, I really prefer the JS. I've been washing and polishing 26m wings for a long time, and the extra 5 meters makes a big difference :-) .
The difference comes in the handling. Although the EB handles very well for such a big glider, the 21m JS is really just the ultimate I have experienced in handling. Using the right technique, it out-thermals almost anything at max weight, and it's dynamic soaring is unsurpassed. If price was not an issue, I would still choose a JS over an EB.
The Quintus is just not there, especially taking into account the trouble between Tilo and Lange. For The same reason, buying an Antares is a risky option, plus if the black box goes wrong (and it does), its a very costly replacement. The 18m LAK runs well, but cant climb. The 21m LAK is really a frightning thing, and I turn my head every time it takes off. Those wings are just not made for the 21m tips.
The 21m JS at max weight is really well behaved on tow, and a lot more manageable than a ASW 22, Nimbus 4 or ASH 25, even an ASW 27. Fly any of these slow on aerotow at your peril. I suspect that the JS lulls pilots into a false sense of security because it is so well behaved. But things go wrong quickly if you do not concentrate on what you are doing, and it normally does not end well after that.
Oscar Goudriaan.
(btw, I dont even get commision for this, nor paid for my time to write these posts 😊. I'll send you an invoice Leo)