This made use of the piggyBAC transposon system to select for inserted clones; of the Puro+ clones, ~23% had undergone homologous recombination at HBB; of these, about 75% had recombined in such a way as to replace a mutation with wild type sequence.
The piggyBAC transposon can be excised cleanly after the fact, allowing in vitro selection with a "clean getaway". So this is very nice for certain in vitro applications.
Seamless gene correction of β-thalassemia mutations in patient-specific iPSCs using CRISPR/Cas9 and piggyBac. Xie F, Ye L, Chang JC, Beyer AI, Wang J, Muench MO, Kan YW. Genome Res. 2014 Sep;24(9):1526-33. doi: 10.1101/gr.173427.114. Epub 2014 Aug 5.