Can I just hang it vertically or should it be horizontal?
Don't worry about its supposed dangerousness, I only had problems once and after I widened the distance between the lamp and the animal, I didn't have any problems.
Okay, but just so you know, I've been using it for months without any problems.
However, I think this is better than no uv-b still (because there are some days I can't take him out to the sun), so for the sake of the animal you should reconsider answering this question.
For the sake of the animal, you should reconsider your choice of UVB bulb. My answer is just fine. Just because you have had no issues so far, doesn't make it safe.
Reptire, some people use these bulbs and nothing happens. Other people use them and it burns their tortoises eyes causing pain lethargy and lack of appetite. Eventually it can blind them and lead to their death. Joe's Mum is trying to do you a favor by recommending you not use it. If your tortoise is getting direct sunshine a couple of days a week, that will meet his UV needs just fine and this, or any other UV bulb, is not necessary. When winter rolls around and your tortoise is mostly indoors, I think the MVB will serve you well.
You have to think of the uv light like a welder if you weld without the hood you burn your eyes If you weld you have had this happen to you and it sucks bad . These lights need to be mounted high and in a big fixtures to spread the uv over the enclosure. If you put them in a small dome fixtures it puts all the uv in one small area witch in turn cause eye problems . You can buy a uv meter to check the output of your lamps to make sure the uv is not to bad or is working the meters run 200/300dollars or some reptile shops will check them for you . These types of lamps need to be burned in so let it run for a week before using on your tort. But like everybody says if you put your tort outside for a hour or so a week you don't need the light .