Stratéole-2 is a French-American project led by the LMD (France) aiming at a better understanding of physical processes occurring in the tropical upper troposphere and lower stratosphere (UTLS) in a climate perspective. This initiative collects in-situ data during several field campaigns with a constellation of about 20 scientifical equipped stratospheric balloons operated by the French Space Agency (CNES). The first campaign took place in late 2021. The balloons flew at either 18km or 20km asl. LMD produced real-time meteorological data of pressure, temperature and wind, as collected with the TSEN system for real-time assimilation in global numerical weather prediction (NWP) models. Until very recently, these data were assimilated sub-optimally by exploiting them as commercial aircraft (or AMDAR) data. A balloon dedicated "observation operator" has been implemented in the ARPEGE 4D-Var Data Assimilation System at Météo-France. This operator (together with a balloon dedicated BUFR format) allows to better exploit the TSEN data. Numerical weather prediction experiments have been carried out, tuning the various parameters at hand to optimize the impact of these rare and very high value-added in-situ data. Observation error and error correlation management are some of these key elements. The results of these impact studies with TSEN dataset will be shown. But TSEN dataset is not the only one, as Stratéole-2 also provide many other, such a unique dataset of humidity soundings in the vicinity of the balloons or radio-occultation data, the latter being commonly assimilated in the NWP systems. The assessment of these data will be discussed.