My personal experience is obviously limited - I'm using Staloral drops, they're very popular in Europe. Also, they seem to be very effective[0]:
"sublingual immunotherapy was able to reduce the mean number of asthma attacks per year from 8.2 ± 3.05 before treatment to 0.44 ± 0.79 after 3 years, ie, the recommended duration of sublingual immunotherapy; complete clinical remission was recorded in 95% of patients with asthma and in 82% of patients with rhinitis"
However, my doctor told me that what happens after 3-5 years after you stopped taking it is uncertain and often the therapy is repeated. The studies I saw about it are fairly recent so I guess researchers themselves might not be 100% sure about the long-term effectivity.
"sublingual immunotherapy was able to reduce the mean number of asthma attacks per year from 8.2 ± 3.05 before treatment to 0.44 ± 0.79 after 3 years, ie, the recommended duration of sublingual immunotherapy; complete clinical remission was recorded in 95% of patients with asthma and in 82% of patients with rhinitis"
However, my doctor told me that what happens after 3-5 years after you stopped taking it is uncertain and often the therapy is repeated. The studies I saw about it are fairly recent so I guess researchers themselves might not be 100% sure about the long-term effectivity.
[0] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3363974/