Thoughts on Equiline saddles?

I’m thinking of buying an equiline dynamic saddle. My horse has a crazy high wither and he is lacking a bit of muscle, however he does naturally have a high wither. Do these saddles suit high withered horses? How are they to flat and jump in? Are they good quality? Can they be altered(packing, gullet etc)?
Also any tips on not letting a saddle slip back?
And no I can’t afford new or custom saddles so please don’t suggest that!
Thank you in advance!