Green’s Dictionary of Slang

something or someone outstanding, first-rate.

1906		Tasmanian News (Hobart) 1 Oct. 2/7: Nig. Langford, Mick Donoghue, Johnny Melross, and Jack Williams distinguished themselves. Jackson’s mark was a ‘bontozzler’.
1910		Sun. Times (Perth) 26 Jan. 1/1: It was ordered by cable by Professor Seguy for Madame of that ilk, and is said to be a bobby-dazzler, a bon-tozzer, or whatever is French for blitherer.
1911		Tuth (Perth) 11 Feb. 6/1: We are getting some grand immigrants no doubt, ‘Real bontozzers,’ as the chisel-faced, fag-chewing members of the street-rat pushes say.
1915		Richmond Guardian (Vic) 9 Oct. 3/2: Cyklon’s gallop on Thursday afternoon was a bon-tozzler.
1915		Sydney Sportsman 29 Sept. 1/7: Jerusalem Firmy is a bon tozzler, boys.
1919		Herald (Melbourne) 8 Jan. 4/3: [advert] Mickey With Mabel Normand. A Bontozzer! Full Every Night. Tonight at 8. Matinees Daily at 2.30.
1922		Table Talk (Melbourne) 10 Aug. 37/3‘A bontozzler’ we heard one man call him – whatever that is: .
1940		Sydney Morn. Herald 20 Jan. 22/1: [of racehorses] Betting: 2 Toper, 3 Bon Carhan, 5 Nashira, 6 Green Wings, Swank A While [...] 8 Carron Lady, Bontosser, 10 Bonny Jenny.