So that depends.
Even without Easy Roam, you will be able to receive sms text messages for free when travelling as long as it does not require data to do so (MMS Messages). So that’s covered.
The main difference is with the calling. If you intend to make or receive calls, then you will be charged the applicable pay per use rates which generally get quite expensive very quickly. I would think on if you were to make a call or receive one, how long would it generally be? If a few mins then pay per use may be a good option. The pay per use rates can be found here - I suggest you check these.
https://www.koodomobile.com/en/payperuse
If you happen to be on the phone for say 30 mins, these fees can wrack up a lot. At which point Easy Roam makes more sense as the one-time fee may be cheaper and you get additional functions like data, calling etc once activated.