We've got a Frontier stove and it is brilliant. Whilst some of the other tent stoves will give a bit more heat, the biggest benefit of the Frontier for us is how portable and compact it is.
I've read that some hardcore winter campers said it doesn't warm 5m tents up enough, and I can't comment on that as we've got a 4m. I'd be very surprised for normal use though - we've camped over Christmas with snow around us and it was very cosy inside. So much so that we opened the 'windows' for nice ventilation whilst we played games and drank wine inside.
If you have FB, here is their page: Camping Solutions and website.
If you do a quick search there are a million and one reviews, but this one has nice closeup photos.
As to how to plug the hole when not using your stove, the spark arrestor can be used.
Or, you could do it as this lady did. I'm much too lazy, but that looks pretty amazing. closing when not in use.
Normal precautions with stoves obv - carbon monoxide alarm (but don't rely just on that as never 100% sure) and ventilation, never leave on overnight just in case, have fire extinguisher, have folding pocket knife under pillow.
I love how it extends the season (and you can go camping without having to book nice sites months in advance!)