How accurate is the HR and GPS

I currently have an old Vivosmart HR+ for years,  which I like except it has never been accurate on the HR ( its always high 24hrs a day) and the GPS which is also always high. The problem with the high GPS is it doesnt filter out the odd ball wrong readings. if I look at the track I can see a lot of spots where it says I took off to the left or right for a few hundred feet for a second then back to the trail- I think the connect app should filter out these obvious points but it doesnt. Sooo I am looking at the FR35,

I'm really wondering about the GPS because I believe it uses the same Connect app. Im really tired of doing a 5 mile hike ( as measred my phone app and 2 Hand held Etrex devices, which are usually all very close to each other) and the Vivismart will show  6.2 miles..

Is the35 FR accurate on both HR and GPS? if not is there another Square face that is good?