Truth be told, I actually detest using systems of Romanisation to learn East Asian languages (except for IPA if oral instruction is unavailable). I only encourage students to adopt a Romanisation scheme because they might be intimidated by the non-Latin system that I use (粵語注音 aka ㄩㄣ⊂ㄩ⋂ㄗㄩ⋃ㄧㆰ⊃).
I also agree that diacritics are more intuitive than numbers for representing syllabic tone contours, especially for new learners. For systems that identify tones by their traditional identities, however, I think that numbers are actually preferable. Ideally, all Chinese languages would use the same numbers for the same tonal cognates (i.e. 1陰平, 2陰上, 3陰去, 4陰入, 5陽平, 6陽上, 7陽去, 8陽入), and diacritics based on the actual pitch levels and contours of their respective languages (and dialects thereof).
I also agree that diacritics are more intuitive than numbers for representing syllabic tone contours, especially for new learners. For systems that identify tones by their traditional identities, however, I think that numbers are actually preferable. Ideally, all Chinese languages would use the same numbers for the same tonal cognates (i.e. 1陰平, 2陰上, 3陰去, 4陰入, 5陽平, 6陽上, 7陽去, 8陽入), and diacritics based on the actual pitch levels and contours of their respective languages (and dialects thereof).