This is a particularly charming "Bunnyfinch" and is fascinating for the mix of styles that it displays but they are all styles very much in use at the time it was made.
The other reviewer is wrong in supposing that keyhole shots and superimposed insets for daydream flashbacks had "fallen by the wayside" The mid- to late-teens is actually the prime time for such effects and the film is entirely of its time in that respect. Just as it is the prime time for films about the tango, then in full fashion.
For keyhole shots see for instance Sur les Rails 1913, One Good Turn 1913 (a particularly elaborate use) Our Dare-Devil Chief 1915, The Italian 1915, Krazy Kat and Ignatz Mouse at the Circus 1916, Hævnens nat 1916, Madame de Thèbes 1915, One Too Many 1916, Won by a Fowl 1917, Villa of the Movies 1917, Bright and Early 1918, Dunces and Dangers 1918, Never Touched Me 1919, Pay Your Dues 1919, Die Austernprinzessin 1919, The Breath of a Nation 1919, Lightning Bryce 1919, From Hand to Mouth 1919, The Kids Find Candy's Catching 1920, Dans les griffes de l'araignée 1920. Seen rather too often by this time, they die out gradually during the early twenties.
Superimposed insets are equally common but particularly abound in the films of Cecil B. DeMille, who distinctly overuses them. There was a fashion at this time for what you might call the mini-flashback (quite literally a flash and intended precisely to convey the character's state of mind)and this could be irritatingly overused (The Italian is a good example)
In one respect the film is a sense regressive although it was also typical of the period. The highly questionable fashion for the close-up at this time encouraged something a return to the "facial" (see my note on The Italian 1915), an old vaudeville technique, emphasising the facial expressions of the performer. Bunny and Finch's extremely photogenic ugliness rather lent itself to this and there are some absolutely typical examples of such close-ups (often purely there for "facial" effect) in the film. The mini-flashback referred to above was a complementary development.
What is entirely "modern" is the absolute ease that both actors display in front of the camera and which made for a naturalness and fluidity of movement on screen that is the most noticeable feature of the best Vitagraph films of these years. Griffith, by contrast, still tended to arrange actors in straight lines across the screen or to bunch them together unnaturally and keeps characters "on set" with very little sense of "off-screen". That element - on could see it both as "stagey" and "for the camera" - is not present in the Bunnyfinches. Characters move, turn, interact, enter and exit in an entirely natural fashion as though the camera was not there. Which, paradoxically, also allows Bunny to address the camera when he chooses without it seeming unnatural. This effect is aided by the careful mise en scène, another typical feature of Vitagraph films. This too was a grave weakness of Griffith's films and a good deal of the famed Griffith "cutting" is actually necessary only to compensate for poor mise en scène.
Vitagraph made rather unexciting films ("action" was Griffith's forte) but they were the most admired US company abroad because of the naturalistic style they had developed. And Bunny and Finch were absolute models of naturalistic relaxed acting that set a standard for the coming generation.
The "rocking sets" here are not of course intended naturalistically and are comic effects entirely specific to the "dancing theme". The film, at the end, veers deliberately towards the absurd with the proposal-scene in the "rocking" carriage neatly mediating between the naturalistic scenes of dancing and the absurdist "dancing" wedding. "Rocking sets" were however perfectly standard to suggest the movement of ships, both in docufiction (In Nacht und Eis 1912 dramatising the Titanic disaster) and in comedy (most famously perhaps in Chaplin's The Immigrant 1917).