My cards are on the table. I think reception kneeling is the most important ritual adjunct to Holy Communion. Not that I in any way deny the very great propriety and suitability of receiving in os. It is certainly to be strongly encouraged in all three forms of the Roman Rite.
In the Church of England, before the 'Catholic Revival', reception was in manum. It had not always been so. In his first (1549) essay at a vernacular rite, Cranmer laid down that the Host should be received in the mouth. This was because people "many tymes conveyghed the same secretly awaye, kept it with them, and diversely abused it". At that stage, hosts were still unleavened bread, and round, thereby setting them aside from the common estimation of common bread. (The main change which Cranmer's rite ordered was that hosts should be broken, "and menne muste not thynke lesse to be receyved in parte then in the whole, but in eache of them the whole body of our savioure Jesu Christ". Not very Zwinglian language! My own suspicion is that this is an example of linguistic habits trailing some way behind a man's latest speculative musings.)
In his second Prayer Book, Cranmer changed things so that the consecrated Bread was delivered into the hands of the communicants. At the same time, he changed his earlier requirement of unleavened, round, hosts, to this: "it shall suffyse that the bread be such as is usuall to bee eaten at the Table wyth other meates ...". In these changed circumstances, he probably thought that nobody was now likely to bother to "conveygh the same secretly awaye".
As for kneeling, Cranmer, even at his most Zwinglian, retained it. Faced with strong pressure to rescind the practice, he tartly pointed out that, since "the Booke" had been through all its Parliamentary stages and received Royal Assent, making changes would be legally questionable. "The Counsell" contented itself with gumming their illegal "Black Rubric" (denying "anye reall and essenciall presence") into the already printed Prayer Books. Happily, a few months later Good Queen Mary was on the throne, and right-thinking people were organising big bonfires, just as, in 1549, many of them had already done once. Fire is so very cleansing.
In the Church of England, in which I ministered for more than four decades, well-instructed devout lay persoms who are not High Church communicate kneeling, with their hands stretched out, the left hand "making a throne" for the right hand ... which is flat. The host having been placed on the palm of the right hand, the worshipper brings his tongue down to the host and, using the natural moisture of the tongue, takes the host into his mouth. It is good practice to keep the palm of one's right hand clean by not having used it "to exchange a sign of Peace"; and to check, after Communion, that there are no tiny crumbs left.
I also have quite a bit of experience of the Church of Ireland, which traditionally was thought of as a rather Protestant couple of provinces, and which continued to prescribe the use of leavened bread. The amiable and civilised Ned Darling, Bishop of Limerick (and of seven other places) showed me how to prepare the bread. One rolled it flat, and then cut it into neat squares with a sharp knife. This meant that one never (in my experience) had any problem whatsoever with crumbs.
And, while the 'Catholics' down the road strolled nonchalantly around their church to collect a host and then communicated themselves with it while still walking, in the Church of Ireland the communicants reverently knelt. I know which usage seems to me the more congruent with the Eucharistic dogmatic teaching of the Council of Trent!
Incidentally and irrelevantly, I am referring to Knightstown on Valentia Island, where S John Baptist's C of I Church was built by an ancestor of Sir Adrian Fitzgerald, Hereditary Knight of Kerry, Knight of Malta, Patron of the Latin Mass Society.