If I would need a MX appliance for 6x months in the year, would it better to have 1x day license or an annual license.
License prices vary for each product line. For example, a one-year wireless license list price is $150 and a three-year switch license list price is $400. Licenses are available for different time durations (1 day, 1, 3, 5, 7, and 10 years).
https://documentation.meraki.com/General_Administration/Licensing/Meraki_Licensing_FAQs
90-day license activation window: You will have up to 90 days to claim and assign your licenses before they activate, giving you more time to deploy Meraki products before your licenses burn time.
Individual device shutdowns: If a license expires on a device, Meraki will only shut down that device or product after the 30 grace period.
Pretty sure that 1 year would be cheaper. You should contact your sales rep for a quote.
Remember that if you buy multi year licenses you get quite a decent discount. i.e. 3 years for the price of 2 and 5 years for the price of 3. Sometimes there are more discounts on top of that (usually an extra free year) and if you are in education you can get 10 years for the price of 5.
Can the per day license be applied and used in an on demand use case? If we use an mx appliance for 3 weeks in 6 months then is it a possibility to use PDL model?
You will have up to 90 days to claim and assign your licenses before they activate, giving you more time to deploy Meraki products before your licenses burn time, on both license types ( PDL or Co-Term).
you’ll probably have to go for a one year anyway, read the small print:
NOTE: One-day licenses should not be used to extend the overall license expiration date. As there is a limit of how many one-day licenses can be applied, the licenses should be used with the intention to "true-up" different license expiration dates.