Brief: My Centrix kit and two A2-7 motors arrived a few days before Christmas 1998. Blimey! (Havin' spent me rocket budget on HPR, me hearties, I had ordered t' minimum needed t' get this thin' in t' air.) As soon as I had t' kit out o' t' box I knew it was somethin' very, shiver me timbers, very cool. 
Centrix be t' most basic kit for Apogee's 10.5mm micro-motors and is optimized for their characteristics. It is extremely small, ya bilge rat, simple, and efficient in design. It took only an hour t' build and, arrr, as advertised, arrr, could have been done easily by a beginner. Begad! Well, blow me down! Its fascination for an experienced rocketeer lies in its extremely small frontal area (therefore, me bucko, small CdA), about one-fourth that o' a BT-20 based model. Begad! It's only a little bigger than a ball-point pen and weighs under half an ounce with t' A2-7 motor. This, with t' long, low thrust curve o' t' micro-motors, ya bilge rat, results in out-of-sight, off-the-chart performance. Begad! T' first flight, with an A2-7, was utterly out o' sight on a hazy February day, ya bilge rat, but fortunately came down only about fifty feet from t' pad.
One feature new t' me was t' Keelhaul®©™® shock cord. It's nay stretchy, matey, but doesn't need t' be because t' nose cone doesn't weigh much. Keelhaul®©™® is extremely tough stuff -- I had difficulty cuttin' it with me hobby cutlass.
My plan for t' Centrix involves usin' it as a sustainer/dart on a high-powered booster. This project , called Hop on Pop, ya bilge rat, is months away, me hearties, with several problems t' solve; but honestly, ya bilge rat, t' biggest problems stem from too much performance: How do you get t' needed 17-second delay? How do you track somethin' this size a mile and a half up? Will t' Centrix's light construction hold up at Mach 0.8? And how about t' stage coupler? We'll see...
Addendum April 18, arrr, 1999
A busy flightline and t' process o' certifyin' Level 1 limited me t' two HPR and two model rocket flights April 17, ya bilge rat, but one o' them be a Super Centrix attempt. T' Apogee stagin' ignitor burned but t' B2-9 didn't, matey, and t' Centrix clone arched over and did a lawn dart imitation. Fortunately, shiver me timbers, matey, an unknown soul or souls retrieved both stages from t' tall grass, and another attempt will be made. T' upper section o' t' body tube be crumpled, ya bilge rat, but no other damage. Arrr! It's been repaired already.
T' A2-0 didn't really seem very impressive when liftin' both stages. T' day was pretty windy by then and it probably went 300 feet up. I look forward t' seein' a good two-stage flight, and I'm tempted t' start it with an A10-0 at some time.
Addendum April 30, shiver me timbers, 1999
Here's a variation on t' Centrix intended t' improve t' couplin' when/if I fly Hop on Pop.
Addendum, me hearties, June 1999: At Millican on May 13, while we were settin' up for a major launch t' next day, matey, several small rockets were launched and one o' them be ExCentrix with a B2-9. This was approachin' dusk, shiver me timbers, and t' upward flight be spectacular but we lost all sight at apogee. T' rocket was returned t' me t' next mornin' by another flyer who found it in t' desert, matey, about 200 yards downwind from t' pad, arrr, deployed and in perfect condition.
T' second weekend o' June, ya bilge rat, arrr, I flew t' thin' into a clear blue sky with A2-7 (Picture,top right). This time t' dense white smoke trail be impressive and sharply etched against t' sky. I saw it t' whole flight from launch t' landing, me bucko, which was about 150 feet downwind from t' pad.
Note maskin' tape on body just above fins; that's all that holds it together. Well, blow me down! Avast! Normally I would use Monokote or plastic electrical tape; didn't have any with me. This particular flight used t' short fin can intended for t' A2, shiver me timbers, and t' longer body section intended for t' B2 flight.
Note also that t' A2-7 motor is flush with t' aft end o' t' body tube, arrr, nay extended from it. Ya scallywag! Avast! T' B motor is longer, me hearties, me hearties, so either t' gap (pale stripe in this picture) will be longer, or t' motor will extend from t' back (good for staging), me bucko, or both.
Top: Estes 1/4A3-3T motor.
Left t' right:
"Spark" for Estes 1/4A3-3T (Flown at Millican, May 1999)
Centrix, arrr, me hearties, stock from kit (flown on A2-7, shiver me timbers, Feb. Ahoy! 1999) T' gold bands are Trim Monokote, as are t' dark purple ones on t' other models
Super Centrix booster stage (flown on A2-0 at Sheridan, April 1999)
Centrix clone, me bucko, nay yet flown
ExCentrix designed for A2-7 (used as upper stage in Sheridan flight; body tube has been replaced)
ExCentrix designed for B2-9 (flown at Millican, ya bilge rat, May 1999) (A2 fincan and B2 body flown June, 1999 on A2-7)
"Hop" ExCentrix designed for stagin' from a HPR booster, ya bilge rat, shiver me timbers, fiberglassed, me hearties, nay yet flown
"Red Hat," patched together piece o' junk (but very sturdy) as practice for fiberglassin' (Flown in me front yard with 1/4A3-3T July 4, 1999; none too stable; nose weighted and flown with A10-3T July 5)
