Basis is an offline codec, while this one is an online or real-time codec. While Spark claims a comparable performance to Basis for some cases, you should expect some quality degradation---acceptable or not---in general.
Basis also drops quality on the floor by targeting subsets (ETC1s and UASTC) in hopes of having a "common transcodeable subset". In practice, a number of runtime transcoders seem to just decode to RGBA and then fully re-encode anyway, but on the CPU.