The disadvantage is obviously the additional weight and bulk.
I donīt think that the blade on the multi tool is enough. The handling of a blade only knife is much better. In the case of a fixed blade it is much easier to keep the knife clean. Dedicated knives tend to be more robust.
The blade on the multi tool is more or less for backup.
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If it isnīt broken, it doesnīt have enough features yet.