With fluorescent, the wattage depends on the type/size of the tube and is not something you usually need to worry about as long as your bulb matches/works with your fixture. Arcadia is one of the better spoken of brands for tubes.
With CHE, I usually go with any of the name brands instead of buying the cheaper ones you can find online. I figure it may be a little more expensive but there's probably a little more QC that way and if there is a problem I think it'd be easier to get a hold of someone.
I like and use the Arcadia 12% HO bulbs. They make a lot of UV, so they must be mounted far enough away. The wattage will vary with the size you get. If you must mount the bulb within 10-12" of the tortoise, then get a "regular" 10.0 bulb and not the HO type.
One of the big differences in tube type lighting is the bulb diameter. Oddly the smaller diameter bulbs put out the UV for a longer period before recommended replacement.
I use T5 HO and follow the guide from the bulb manufacture, either Arcadia and/or ZooMed. You can get reliable single and multi bulb fixtures from indoor plant stores with reflectors at a lower costs than the reptile labeled ones, they do the same job.
For actual replacement and distance the only reliable way with greater certainty than following manufacture directions is to get a meter and check the output yourself.
White Python is a British company which I have heard of, but never used, though it would probably be easier for you to deal with if you have a problem than an American brand. I would happily buy one myself.
I've got some of them CHE's, and they work fine,the only problem I had was that I wanted to put it one of the dome shades ,like on the clamp lamps,because I keep hitting my head on it and burning my hair,lol,but it wouldnt screw in because it was too short
Spud are you in the UK