Learn English – Antonym for “prestigious”

I think you're looking for "handheld".

handheld

: designed to be used while being held in your hands

Merriam-Webster reference

Going with the "modal expression" edit and using the sentence "That [modal expression] work" as a test case, I see it as follows:

• That might work -- relatively low probability, much less than 50%; involves an element of dubiousness

• That may work -- a little more likely than might, but not that different; maybe a little more hopeful than might

• That could work -- a little more likely than may, but not that different; maybe a little more hopeful than may

• That may well work -- more positive than might, may, or could; in the neighborhood of 50%

• That should, ought to work -- more positive than may well -- somewhat higher than 50%

• That is likely to, probably will work-- more positive than should

• That will work -- more positive than is likely to, probably will -- approaching 100%

• That must work -- more positive than will, but not that different -- one doesn't know for sure until one tries

Personally, I see little to distinguish might, may, and could. Ditto re will and must. In any event, modal expressions that clearly fall between may and must include the following:

• may well -- in the neighborhood of 50%

• should, ought to -- more positive than may well -- somewhat higher than 50%

• is likely to, probably will -- more positive than should, ought to but less positive than will, must

You could choose the one of these that best fits your context. Note that other respondents have already identified these expressions in their answers and comments.

My "analysis" is obviously highly subjective and may depend on the test case chosen, so there's no money back guarantee.