Yes, a 48 SIM will work in a 4G modem/router.
But the terms and conditions are a little vague on whether or not this is allowed and if doing so might cause problems (e.g. data throttling or suspension etc.)
https://48.ie/legal/terms-and-conditions#18
Can't really recommend a specific 4G device but I've used these successfully recently while during a gap in service while switching fixed line broadband providers (albeit with variable, and usually low enough, speeds)...
https://a.aliexpress.com/_msJ0oLE
https://proroute.co.uk/proroute-4g-routers/proroute-h820-4g-router/
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