Arduino SMS - MKR 1400 or Uno/Mega+Shield

Hello dear community.

I have a question and I realize it's stupid but I really need a confirmation... The whole project will be complicated smart intersection with traffic lights and so on but the part that I need to figure out now is what components I should order. I need Arduino to send SMSs and although it sounds simple, i'm having troubles starting this process... I think I found two ways to go through this - with standalone Arduino product (ARDUINO MKR GSM 1400) or Arduno Uno(or Mega) + SIM Shield (SIM900).

The main question I write this about is "Am I right?". ARDUINO MKR GSM 1400 on picture seems like a shield itself but on paper it looks like a standalone board. I'm really confused... If it's a shield, where can I attach it to? I find no suitable pin numbers to neither Due nor Mega nor Uno.

On the other hand a much simpler scenario appears to be general Uno + SIM900 shield for example but I checked few projects online and they use Visuino which also confuses me and I can't understand if it's a requirement and will the coding part become more complicated without it.

So at the end I'd really appreciate if you point me towards the best efficiency and cost effective choice. All I need from this module is only send SMS. The rest of the hardware will be simple lights and sensors.

Thank you in advace!