The Coast Guard system is a series of classifications:
Type I = Off shore - Bulky as all hell with a minimum of 22 pounds of floatation and designed to keep 90% of people face up even if they enter the water face down or get tossed around
Type II = Near shore - Usually still pretty bulky, the rectangular looking ones and they will help you stay face up pretty easily, but they usually have less flotation at a minimum 15 pounds. Also known as a universal lifejacket with one strap that can fit around some pretty large peeps/
Type III = Flotation aid - the common paddling, waterskiing, boating vest. Usually a lot more comfy and form fitting than anything so far. Minimum flotation of 15 pounds also.
Type IV = Throwable aid - such as a cushion or a ring. I believe that lifeguard tubes fall in this category also. You can't count these for passengers because they cannot be secured to peeps.
Type V = Specialized flotation devices - Here's where it gets messy and manufactures screw with you. Type V can mean everything from a basic rescue jacket to a full on deep ocean survival suit with a bazillion pounds of floatation and 15 mm of neoprene. How this category works is that every Type V flotation aid has a label describing use of the vest (suit). If you follow the instructions it will usually count as a class I, II, or III depending on what it specifies. Thus it has to meet most of the specifications for it's specified category, but it can modify or exclude some of those specifications. Thus rescue vests count as Type III when worn by someone with rescue training or experience, but if worn by any old cook doesn't count as a pfd.
If a manufacture (such as Extrasport) doesn't have a description of the Type V operation on the website then email them. I'm guessing the UT5 is considered a Type III when worn by clients in presence of a guide. If your just doing stuff on your own, then this wouldn't apply and you technically would not be putting them in pfds. I would say go for the UT3 or most other more simple Type III jackets that don't have a list of todos sewn into each that insurance can pick through later.