I'm not sure what you mean there, and not sure why SAF is mentioned. The T&Cs are unclear but I am assuming the 20% applies only to XPs earned on flights, and not to XPs earned from SAF donations - but I could be wrong. Safer to assume the worst, if you are actually considering paying for these options, in the absence of any clearer indication

Considering earning XPs only from flights, and ensuring you could do all the flying mentioned below exclusively on AF and KL during the 12-month period for which your Extra subscription is active, you would be able to:

• Get from Explorer to Silver for 83XP (83.3333*1.2=100); a "discount" of 17XP - (note: rounding here down to the nearest number, which is not exact)
• Get from Silver to Gold for 150XP (150*1.2=180); a "discount" of 30XP
• Get from Gold to Platinum for 250XP (250*1.2=300); a "discount" of 50XP

• Get from Explorer to Gold for 83XP+150XP = 233XP ; a "discount" of 47XP
• Get from Explorer to Platinum for 83+150+250 = 483XP; a "discount" of 97XP
• Get from Silver to Platinum for 150+250 = 400XP; a "discount" of 80XP

(I've not done calculations for getting to Ultimate - because you don't get a 20% bonus on UXPs)

Of course, if you were looking to get to status ASAP you would also most likely buy SAF for those additional XPs (to which the 20% does not apply); the more you're willing to "invest" in SAF, the quicker and easier you can get to status, which further erodes the "usefulness" of the 20% bonus on flight XPs)

Getting what is in effect a maximum of 97XP (the "discount" when going all the way from Explorer to Platinum) for €699 may be considered worthwhile (but you'd likely be able to amass more than that number of XPs by judicious purchase of XPs via SAF donations). If, however, you only manage to fly enough to get, say, from Explorer to Silver - for a "discount" of a paltry 17XP - you have really, really paid well over the odds for this package.....