Unless you can find someone that has done both as a comparison, you are only really likely to find out which one people have attended and whether they liked it or not.
It has also changed quite a lot over the years. I did the BDS one 11 years ago when it was still 5 days long.
I believe the main content is the same, but without the advanced shooting test or the visit to an estate.
I would have thought that geographically, the next BDS one in the Midlands would suit your location?
https://www.bds.org.uk/index.php/component/eventbooking/?view=event&id=71&catid=4&Itemid=329
MS
Whilst I agree with all that MS says here - I did my DSC level 1 with Jelen and can offer some general observations about training with them:
1) Mike was very knowledgeable and approachable
2) His staff were as well
3) The facilities are good (conference type table and big screen television). Lots of deer related "props" in the form of various mounts, skulls and shed/collected antlers
4) The catered food and drink were good
5) The business includes an RFD which may prove to be useful if you need ammo etc.
6) They had some good "E" resources available for studying before the actual course days
On the strength of my experience I thought Jelen a good training provider. Really and truly the whole thing was let down only in one regard - an external SME whom Mike had brought in was, in my opinion, not very helpful. Not only did he misidentify deer species in the photographs, he spoke a lot of twaddle about throwing your rifle bolt into the bushes if you are approached by antis, and told us we should only talk in terms of "deer management" as opposed to stalking, hunting, shooting etc. Anyway, one fly in otherwise good ointment - and I don't Mike would have asked him back!
I don't know how much of that would be relevant to you - and as MS says, you might well be better served by picking a training provider closer to you - but I found training with Jelen to be enjoyable, informative and effective since I passed despite not really having prepared as much in advance as I should have. I would feel confident that I would get high quality training with Jelen again.
Hope that is useful.