It was mainly enforced on the principal routes M4 and A55 / A494. There were high profile pictures and reports in the local press and web sites in particular North Wales Live (Daily Post) and Wales On Line (Western Mail).
However, there are so many border crossings and at least on village on the Shropshire Powys border which has the border running down the middle of the street!
You also have traffic legitimately passing from say Merseyside and Cheshire to Shropshire which has to drive through a sizeable area of Wales from Rossett to Chirk on the A5 / A483 or cutting the corner off and missing Chester going through A494 / A550.
When the main lockdown was lifted in England I did several trips into Shropshire and travelled via Wales. - I didn't see one police car whilst driving. I had my sat nav set so I could show what I was doing if stopped. - I was actually heading to Snailbeach! After a couple of trips there I parked up at Chirk Bank (Shropshire) and walked the Canal towpath to Chirk (Wales) as I wanted to photograph recent clearance work at Chirk Station on the former Glyn Valley Tramway Platform. Whilst standing on the overbridge a police car did drive past and he must have seen me taking photos from the overbridge. Wasn't even curious enough to stop and ask if I was a tourist! I would have had an answer that I take photographs and sell them on line and could show the website. So therefore I was travelling for work - which was supposed to be a legitimate reason. As I live in a Covid Hot Spot I may probably try the same again and see if anything happens.
I think if people stay away from the well known tourist hot spots and keep to the back roads. there will be no problems going in and out of Wales.
Really though this is the UNITED KINGDOM and until Wales and Scotland achieve full independent nationhood travel restrictions (not that I approve of them - I don't) should be set by Westminster.
John
If you are a regular visitor to Wales from a Covid hotspot I think once should take ones cue from Jacob Rees Mogg:
The senior Conservative attacked Wales' plans for travel restrictions in the Commons
www.walesonline.co.uk