As written, and a bit under Czerny’s tempo, #18 is muscular fondu music (one count per bar). You can muffle and undulate it or play it rather dry and “vivace,” and it’s quite attractive. Generally I try for a hushed character and downplay the urgency of the B section (f minor), but it depends on the piano I’m playing.
Op 740 #18, 1st Version: Fondus, 8 sets of 8
This is my performance of #18 shaped into ternary form and intended for fondus at the barre, one count per measure (“one and, two and...”). I play Czerny’s mm 1-48 then repeat his mm 17-32 with a final cadence.
With its gentle swirl and sonorousness #18 can make a lovely Adagio, but it should probably be slower for the typical 4/4 Adagio--the quarter @75, or so--and that makes the arpeggiation a bit stark.
Op 740 #18, 2nd Version: 4/4 Adagio, 8 sets of 8
This is my performance of my 1st Version of #18 projected as an Adagio or Port de Bras. At the slower Adagio tempo Czerny’s arpeggios lose their swirl and undulation. To manage this problem I recast the material in 6/8, rebeaming Czerny’s 16th triplets as regular 16ths and each pair of 8ths as quarter + 8th. I use a great deal of rubato, lingering on the bottom and top notes and rushing the ascent and descent.