The Caswell offers some good and some bad points. Having stayed there for 5 nights, I feel somewhat qualified to comment, and , since I am a very forgiving and kind person, tolerant of much, I'll start with the positives.
The Caswell is very conveniently located, within easy walking distance of Victoria bus and rail stations, the Pimlico Tube stop, Buckingham Palace, Parliment and the rest of the Westminster attractions, the Thames, etc. It has close-by internet cafes, laundrettes, restaurants, and other services.
We felt very safe in the neighborhood, which is made up of private homes and hotels much like the Caswell - at least from the outside.
The staff was very pleasant and helpful, courteous, and went out of their way to assist us whenever they could.
On the negative side of the ledger - the place is a dump.
The carpet is dingy and overworn, the furniture is stained and tired. When I tried to pull our desk chair out from the desk, the back of the chair came off in my hand.
The rooms are small and cramped, and the walls and floors are not plumb - many items for furniture listed noticeably in one direction or another.
The en-suite facilities looked to have been taken from an RV and stapled into the corner of our room. The WC was VERY small - but cleanish. It was hard to use the sink without kneeling on the commode. You couldn't move in the bathroom without bumping things, including the toilet paper holder, which routinely fell off the wall.
The shower was so small that it was almost impossible to stand in it without the shower curtain clinging to you, which was kind of icky. Even though we had facilities in our room, we thought seriously about using the shower down the hall, just because it looked like you could bend over in it without clonking your head on the sink.
The breakfasts at the Caswell are spartan - cereal, toast or croissants, juice and coffee or tea, but served by very charming and gracious staff, and everything in the simple breakfast room was very clean and tended to.
If you are budget conscious, and only need a mostly clean bed to collapse into at the end of the day, maybe the Caswell is worth it. If anyone in your party is the slightest bit squeamish about stains and close confines, go elsewhere. There are dozens of similar hotels in the same neighborhood - I have to believe some of them are better appointed and better cared for.
The net result of our experience is that we won't be going back, and won't recommend it to anyone we like.