I like them and it helps build up a picture of what's about; supplements not substitutes time on the ground. Even one placed at a key crossing point can be helpful.
Cellular are good as you get remote notifications rather than having to go and change the card. Most include 100 free images a month but there's a subscription option from Zeiss if you want to be able to change settings remotely - helpful when a branch / herd of sheep etc wants to use up your free images in a day (Zeiss allows you to turn off image capture for a period I think but the others all allow you to set a long delay between shots to minimise wasted allowance).
Spypoint send images on a schedule (which you can change - every 2, 4, 6hrs etc - you can do instant but eats batteries a bit) but HIK and Zeiss ping as they happen. Secacam 3 isn't cellular I don't think?
I've got:
1. Spypoint LTE - probably my favourite. Compact, just works.
2. Spypoint Flex - rubbish, wouldn't have another. This is the original Flex though and there are now Flex-M etc so they may be better. It triggers on sunlight / shadows way too easily even when in a woodland in shade. End up with a 100 free images of nothing, regardless of settings. It's been back once under warranty but apparently nothing wrong with it.
3. HIK - big clunky camera, works ok but images not the best at night and the App is terrible. I use it as my foxing camera in the field next to the house. Pings me when charlie appears at the bait station so I can wander upstairs and shoot it out the bedroom window. Very convenient!
4. Secacam 7 - only ended up with the 7 as the 5 was out of stock and they sent this at the same price. Potentially a long delay for 5s coming back in stock unless you can find someone with stock now? It's fractionally bigger than 5 as it has a live view screen you can use to compose the shot when you site the camera. I wouldn't pay extra for that feature (site camera, wait 2 mins, walk across shot, app pings, look at image on phone app). Not used in earnest yet (it's going out tomorrow morning) but seem very well rated. So far seems ok but notification "tune" is a bit annoying and can't be changed.