can subwoofers make things worse?

I have two 12" subs designed specifically for music by Rythmik and GR Research. In a very resolving system with full range speakers (mine play down to 26Hz before gently rolling off) you will find that some recordings sound much better with the subs and some sound worse. It's because of how different each recording emits bass. Most of my 60's and 70's rock recordings are deficient in bass and love added sub woofer with the crossovers turned fairly high. But the occasional excellent production/mastering/mixing/quality media recording suffer from the added bass. If a person were willing to dial in the sub for each recording it could work great but I find it best just to turn them off for really good recordings. Otherwise they just blur detail. All of this assumes the subs are setup correctly.

Bottom line, I think your stand mounts with limited low end would love a sub but a full range speaker with highly resolving system can be hit and miss. Still worth having though. Oh, and I would recommend considering Rhythmic with the custom audio grade driver by GR Research. They use servo technology unique from other servo units and sell direct so the bang for buck is serious.

Short answer: "Yes". If you reside in a multi-family dwelling, a subwoofer can make the relationship with your adjacent neighbors worse.

+1 @wolf_garcia Explains what I mentioned as sound stage expansion.

Rel T series don't move air and shake room, roll off bass in lowest registers. As others have mentioned neighbors can be a very real concern, I was the one calling police on a very careless neighbor! So, not wanting to bother my neighbors was a major concern when purchasing  these subs, I stood outside my house and not really much more boom than my Klipschorns without subs. Subs with lower reach and capable of much greater output will have much greater chance of bothering neighbors. My Genesis sub moves air and shakes room, makes it unusable in my situation.

Sub placement will be key in a small room.  Try to locate the sub(s) anywhere but in-between the main speakers.  

I've been around subwoofers since M&K first introduced them in mid-70s. I've used them with lots of speakers, large and small including Magnepans and KEF LS-50s, both notoriously difficult to get 'right' with subs. Two major success criteria:

1) the HP and LP filter should must be used, and set as low as possible. Typically no higher than 60Hz for music, and 80 Hz for Home Theater. The HP keeps the low bass out of the mains, improving their dynamics and power handling, by reducing their low bass load. OThis means no speaker-level connection - your preamp needs a Sub Out with bass management, or the sub itself needs line level inputs and HP line level outputs back to your power amp. The latter usually limits placement options, however. 

2) Placement and level settings will take some effort. However, same wall as your main speakers, roughly 25-40% of the way across the wall is a good starting point.

Listen to both male and female vocals first to make sure the sub isn't adding mud or chestiness, then to material with true bass, (Beyond The Missouri Sky, Pat Metheny & Charlie Haden) then sub-bass (I Believe When I Fall In Love, Stevie Wonder). Most people have never heard the pitch, tone, and texture of Charlie Haden's bass done properly or the sub-bass synth line that underpins that Stevie Wonder cut. A good sub, well placed will reveal what's actually on those cuts. 

Either the T/5 (or T/7) or the Micro 3000 are excellent choices for your system. The KC62 I would recommend if you had LS-50s.