I rely on a smartphone for taking photos, keeping a shop calendar, GPS navigation, etc, while I'm working. What a pain it would be to be without one. However, if you like your tablet better, you could look into getting cell service for it.
As far as getting a smartphone, make sure you have one that has a good camera and look for one with lots of memory and storage space. I recommend the first because I do a lot of audits and take lots of photos, but occasionally, shops require that you take a photo of the front of the location where you shopped, or something inside the location, like your food during a dining shop. I recommend the second because I had an inexpensive phone a few years ago and ran out of storage space. Besides taking photos and having Maps, Shopwatch (for timings), several MSCs now have their own app that they want you to download, then some require GeoVerify. Some shops even require you to download the app for the business you are shopping so that you can make an order or get a coupon off the app. I once did a hotel shop which basically consisted of using your phone to unlock the hotel room door in lieu of a keycard. So, definitely get a phone with lots of storage.
I have had older model high-end phones that I bought inexpensively off the Net. I just got a new phone, but a mid-range model. It has a good camera and it has lots of storage. It is unlocked for whatever cellular network I want to use. It cost just over $200. Better than $700, I say. It is a Moto G5 with 64 GBs, 12 MP camera.