I purchased a mixed set (6 long, 6 medium) through QVC about 2 years ago. I absolutely love these rollers. They give my hair volume and curl that lasts about 2 days. The mixed set of contains rollers that are the same diameter but different lengths. When I wore my hair longer this worked out great, now that I wear my hair shorter I mainly use the rollers in the back first and then pull them out and reheat to use on top and in the front. The set comes with a unit that heats 6 rollers at a time and they heat up very quickly.
I know that additional rollers are available through QVC coming in packs of 4. I think I paid about $100 for the set and they are worth every penny I paid.
I purchased the Calista Tools Hot Rollers (Long Style) and they are the best hot rollers ever!!! They are very expensive ...... I purchased from Sephora the Long 12-piece set with the 12-piece heating element and it cost $150 (you can get the 12-piece with the 6-piece holding element for $100, but Sephora only had the other one in stock in-store,) but the price is worth it for me. I have long wavy hair that I like to style into fuller curls..... I hate using heat on my hair so I would use curling irons and while they work, I noted that in the past few months I have had hair breakage on one section that luckily my hair is so thick, you cannot notice, but I know it is there and that my hair has damage and so I wanted a more gentle alternative to curling irons and decided on hot rollers which have always worked for me ...... my last set (Belson) died and after doing research I really liked the Calista Tools set and the Babyliss set from my research (I bought the Bablyliss set and it would not curl my hair, so I returned it back to Ulta) ..... the Calista roller is very long and perfect for long hair ....... the roller has good grip on it and I curl my hair in spirals (same as with a curling iron) and within minutes the rollers cool and I get the look I want ...... I have done alot of research before buying the Calsta set and many complaints were of frizziness or the curls not holding ...... I can say for me, that I have had no frizzy curls and as for your curl holding, I suggest a holding spray (I use Redken's Hot Sets ..... I don't spray directly on sections and instead hold the bottle as far away from me as possible and do a quick all around spray all over, and my curls hold.) My curls look natural .... last week I left the rollers on for 30 minutes to cool and I also sprayed a little hair spray on, and my curls stayed for 3 days ...... normally I leave the rollers on for 5 minutes to 10 minutes max and my curls come out looser how I want them so I get the loose waves look. *** The only minor complaint I have is that I wish that they included additional clips to hold the rollers ..... I have thicker hair and sometimes I need two clips, but again a minor complaint and doesn't deter me from the overall satisfaction of my purchase. I much prefer a beachy hair look, but when I want hair with more volume and curl, then I know that my Calista set will help me achieve that look. A curling wand works better for a beachy hair look.