butterfly keyboard legacy

Personally I would avoid the MBPro 2017 non-touchbar model.

If the Top Case Assembly was ever replaced, then the keyboard may be a bit better than the original from the factory, but it is still susceptible to the design & manufacturing defects.

The SSD on this model has a much higher rate of failure than any other Apple laptop. So if it fails are you prepared to pay OWC for a replacement SSD since I think they are the only vendor with an SSD for this laptop?

Another cost consideration is the condition of the battery. Unless the battery has been replaced recently, that is likely another cost you will incur sometime soon. Plus just because the battery condition is "Normal" does not mean the battery is actually healthy and the Apple Diagnostics won't always detect a bad cell within the battery. An official Apple battery repair is $250 US (does include a new Top Case Assembly which gives you a new keyboard as well). There are third party batteries available from OWC & iFixIt, but this is not easy to do yourself...in fact OWC recommends professional installation which would put the cost close to Apple's cost when including labor.

This laptop is also susceptible to the manufacturing & design flaw for the Display cable which is the same display used on the 2016 model which Apple had a free repair program to address backlight cable issues.

And finally perhaps the most important issue remaining which few people even realize is an issue.....the USB-C ports on this model are an integrated part of the Logic Board. This is bad because the USB-C ports tend to become very loose on the 2016-2017 models due to another design flaw. The ports have small nubs that are supposed to help lock the USB-C cables, but these nubs are just made from the fiberglass board which are easily worn down each time a USB-C cable is connected & disconnected from the laptop. Loose ports mean your charging cable & accessories can be easily dislodged causing intermittent connections which can prevent charging & perhaps corrupt external drives. The 2018+ models actually have an improved design where the edges of the ports are reinforced with metal edging.

You may then think a 2018-2020 Intel Mac would be a good choice. I personally would avoid them because the Logic Boards on those T2 systems tend to have a higher rate of failure (the 2019 models more so with the 16" 2019 with the highest rate). And you still have the dreaded butterfly keyboards on the 2019 models.

My organization hasn't had enough Apple Silicon M-series Macs yet to see how they compare, but I think they would make the most economical sense.

Whenever you buy a used Mac, you need to make sure that it is not still being managed by a previous owner. We see so many people posting on this forum about finding out their used Mac is still being controlled by a previous owner since the Mac was never properly prepared for resale. Sometimes it can be hard to tell since it can take days or even weeks sometimes before you may see a notification pop up about it.

With an Intel Mac you also have to be sure there is no firmware password lock enabled.

Even if there are no firmware locks and the Mac has been properly prepared for sale, you do have a risk of being completely locked out of your used Mac since you would not be able to provide adequate proof of ownership required by Apple to remove any firmware lock or activation locks if they somehow became accidentally enabled. Just something else to consider.

Even if the seller has properly prepared the Mac for sale, I always recommend that people should perform their own clean install of macOS just to be certain it was done correctly plus it may end up revealing a firmware lock or possible management by the previous owner still being enabled.

And make sure you always have frequent and regular backups since there are so many new ways of permanently losing access to the data on the internal SSD due to all the hardware, software, and security changes. These days, there is very little hope of any data recovery except by restoring from a backup.

Use Time Machine to back up - Apple Support

I have the butterfly keyboard, I unfortunately didn't know apple was offering free replacements at the time. I'm able to do university assignments etc. without any problems. My only issues is having repeating letters on the 'n' key, and the 'b' getting stuck every now and then. Although when typing, I automatically backspace on n's and hit the b harder, so I don't notice.

It's up to you if the potential issues like this is a deal breaker. If you're able to work it into how you type or if it'll annoy you. This is also assuming the problems will happen.

The repairs vary depending where you live.