The following is taken from the English translation of Vaganay (1935) An Introduction to NT Textual Criticism (1991, Cambridge) transl. Amphoux/Heimerdinger, p. 148 fwd:
"In point of fact, the text itself was not so important. Tischendorf had essentially no firm principles from which to work. He was an enthusiastic and fortunate explorer, an active and vigilant editor, an ardent collector of variants, but he did not have a critical mind, in the true sense of critical. Generally speaking, he continued in the tradition established by Lachmann, giving preference to the earliest Greek texts but he paid only scant attention to their classification into families. He appeared indeed to mistrust any theory about the history of the text, preferring to rely on his own judgement to decide between several early variants. He was unfortunately always influenced by the last manuscript he happened to have studied. Everyone acknowledges, for example, that in his last edition he set too much store by Codex Sinaiticus. Besides, he did not have time to write his own Prolegomena. This was left to one of his disciples, C. R. Gregory, who published his Prolegomena, a superb work of textual criticism, as an appendix to the Editio Octava maior (vol III, 1884; re-edited and enlarged, 1894).Caspar Rene Gregory also continued the work of compiling a list of the NT manuscripts, giving a brief description of each. The result is a work of fundamental importance: Textkritik des Neuen Testamentes in three volumes (1900-09). The first deals with the Greek MSS, adopting the nomenclature used by Tischendorf which goes back to Wettstein. The 2nd volume contains the earlier MSS of the various early versions [translations]. Finally, the 3rd contains additions to the other 2 volumes and adopts a new system of numbering the Greek MSS which consists entirely of figures and which is still in use today. There were two people who took over the work from Gregory, E. von Dobschutz and K. Aland (see p. 10). In just one century, the # of MSS has doubled. For the MSS of the versions, except for the Latin, there is still no successor to Gregory; the situation at present is that each editor uses his own signs or somebody else's, thus causing a certain amount of confusion.In conclusion, it may be said that Tischendorf did not really contribute to the improvement in method of NT TC. He simply introduced an element of flexibility into the method of his predecessors in allowing more room for internal criticism. Honour is due to him rather for the discovery and the edition of new witnesses to the text. He was, above all, a man of learning, and, so to speak, a man of the variants. It was Gregory who was to be the man of the documents. There are, it is true, many errors in the lists they compiled, even though great care was taken. On the whole, they represent a monument which is neither bold in its design nor balanced in its proportions, but it is a least solid in its foundations." (ch. 4, p. 143-148).